 Hello and welcome to the session. My name is Mansi and I am going to help you with the following question. Now the question says a wooden bookshelf has external dimensions as follows. Height is equal to 110 cm, depth is equal to 25 cm, breadth equals to 85 cm. The thickness of the plank is 5 cm everywhere. The external faces are to be polished and the inner faces are to be painted. If the rate of polishing is 20 paisa per cm and the rate of painting is 10 paisa per cm square, fine the total expenses required for polishing and painting the surface of the bookshelf. Now this is the figure given to us in the question. So let us start with the solution to this question. First of all it is given to us in the question that area to be polished is the external surfaces. So we have to find first of all area to be polished. First of all we have to see what all areas are to be polished. The external surfaces are to be polished or external surfaces are this portion, this portion, the side two portions and one back portion along with this portion plus this portion. So that will be first of all we will see the back portion that will be 110 x 85. So area of the back portion will be 110 x 85 that is length into breadth plus we see it for the upper most portion and the bottom portion that will be 85 x 25. So we have twice of 85 into 25 and we will consider the two side portions that will be twice of 110 into 25. Now we will consider these portions 1, 2, 3, 4, this is 4 times of. Now we see that thickness is 5 that means we will consider 85 minus 5 minus 5 becomes the length of this portion. So the length of this portion is 75 and the breadth is 5 that is given to us and since it is 4 times so that will be plus 4 into 75 into 5 and then finally these two portions that will be twice of 110 into 5. So area to be polished is this. Now we need to calculate this. We see that 110 into 85 will be equal to 9350 plus 2 into 85 into 25 is 4250 plus 2 into 110 into 25 is 5500 plus 4 into 5 into 75 is 1500 and 110 into 5 into 2 is 1100 centimetre square and this sums up to 21700 centimetre square. So we see that is given to be 20 paisa per centimetre square plus the polishing is 20 paisa. Back in the figure the inner areas are to be painted so we have two portion of the first shelf, upper and bottom portion of the second shelf and three third one. So we have 6 becomes 20. So we will have this portion that will be for this portion. Now the dimension is 110 but here we see that thickness is 5 so 5 plus 5 plus 5 plus 5 that means twist 20 that is 90 will become the length for this portion and since we have to find the area for similarly this side also so we will have the back portion that will be 75 into 90 because this is given to us the breadth is 85 thickness so we get 75 got in the earlier part will get this length as 90 centimetre and then we will have 75 into 90. Now this will be equal to 9000 plus 3600 plus 6750 that is equal to 19350 centimetre square is given to be 10 square that means for 1 centimetre square it is 10 paisa, 10 centimetre square in the terms of rupees we have 1 9 3 5 0 into 10 divided by 100 we see that 1 0 gets cancelled with this another 0 gets cancelled with this and we have rupees 1935 therefore 935 and that comes to this question is that the total expenses required for polishing and painting the surface of the bookshelf is 275 so I hope that you understood the question and enjoyed the session. Have a good day.