OK, we're going to find the anti derivative. So we're going to get DSDT equaling negative KT plus C1. We were given DSDT is 80 when T is 0, so our C1 is 80. Now we're going to find the original S by taking the integral again. So s = -K / 2 T squared plus ADT plus C2. Now we're given that S is 0 when T is 0, so our C2 is 0. So s = -K / 2 T squared plus ADT. Part 2 says figure out what happens when DSDT equals zero. Well, DSDT equaled negative KT plus 80, so zero is going to equal negative KT plus 80. Take the KD to one side, solve for T so we get 80 / K Part three says what happens when S is 200? What is our K value? Our K is a constant, so we're going to put 200 in for us and we're going to put 80 / K in for our T and we're going to solve for K and we get K = 16.