How I got my answer is that you write the numbers and the difference of the each 2 numbers. When you see the pattern is 5, 10, 20, and it might as well be 25 because you are going to start all over with the pattern
So on Wednesday, he did 4 jumping jacks. On Thursday, he did 5 more jumping jacks than he did on Wednesday (9 total ). On Friday, the difference between Wednesday and Thursday doubled, and it has a difference of 10 new jumping jacks(19 total). On Saturday, the difference between Thursday and Friday doubled from 10 to 20, (39 total). So if the difference keeps up, which it should, The difference between Saturday and Sunday should double from the diffeerence from Friday to Saturday (a difference of 20). So if the difference is doubled, it will be a difference of 40. so 39+40=79.
