 In this video we want to find the base of a trapezoid given the fact that we know one of the bases and we also know the height and an area. So we want to find the other base. So first off, let's rewrite the area formula for a trapezoid and we'll substitute in the value of the area, one of the bases, and the height. Now the nice thing about multiplication is I can multiply in any order I choose. So instead of 1 half times 5 plus B times 6, I'll rearrange that as 57 equals 1 half times 6 times the quantity 5 plus B. And now 1 half times 6 of course is 3, 3 times the quantity 5 plus B. Then let's distribute that B, or sorry, distribute the 3, 3 times 5 and 3 plus B. So we get 57 is equal to 3 times 5 is 15 plus 3B. Now I'm kind of running out of room so I'll just shuffle over here. So if we subtract, let's say let's subtract 15 from both sides, then I get that 3B is equal to 42 and divide by 3 on both sides and we get that that other base must be 14, 14 units. So problems like this aren't too bad. You just got to kind of use that area formula in reverse. Alright, we solved for B.