I'll have Martin as X and Melvin as Y.
So the equation for X is, 15(starting point) and +5 every set.
Here's a table
________________
The amount of sets|Lbs -------->This one's for Y
__________________ ________________
0 | 15 0 | 60
1 | 20 1 | 50
2 | 25 2 | 40
3 | 30 3 | 30
4 | 35
On the third set, tables help. I'll do the first question in the comments