Well assuming x is hours, answer D is correct. This is because we are taking amount of hours as the input and the grade they got as an output. So, assuming that every unit step means an hour, for each extra hour someone studied, they got 9.6 more points. The +65.8 means that usually someone who didn't study got a 65.8 because when x is 0 (0 hours studied), what's left is 65.8