Hi,
It looks like they want you to look at the graph for A and B to first determine the inputs, then using those inputs draw s1 through s4 and C4 as you did for the 2nd set of inputs which was 10 plus 10. The first set is 0 plus 0, the second set 10 plus ten as you did, and the third set is 3 plus 3. You should draw a line higher when the output of that s is a 1 and a line lower when the output of that s is a 0. Right now they show all the s being low so you have to change that.