 This problem is pretty good because it emphasizes how to write our scientific notation when we only have one significant digit. So as you can see, all of these numbers when we put them in scientific notation are going to have negative exponents because we're moving the decimal place to the right. On the first one, we're moving it one, two, three, four, five, six, seven, eight, nine times to behind the first significant digit. And you can see there's no other digits behind that, so there's only going to be one significant digit in our answer. So it's going to be one times ten to the negative ninth seconds. In B, there's three significant digits in the given number, so there's going to be three in our answer. So we just move it one space behind the first significant digit, so we got 1.43 times ten to the negative one seconds. In C, we're going to have to move it twelve spaces to the right to be after the first significant digit. So it's going to be one times ten to the negative twelve seconds. And hopefully you can see, especially in that problem, and in A, that the zeros become really cumbersome. So writing things in scientific notation is very helpful. And then for D, same thing, we're going to move the decimal place six places to the right. So we're going to have our answer be one times ten to the negative sixth meters. So make sure you're putting the right number of sig figs in there, the exponent to the negative, and always make sure to have your units if you need them. Okay, let me know if there's any questions on this one.