A: 5x-3y=70
B: 3x-7y=60
Multiply each equation by the coefficient of the same variable in the other equation as the first step in eliminating that variable:
3A: 15x-9y=210
5B: 15x-35y=300
3A-5B: 26y=-90, y=-90/26=-45/13.
Now repeat this for the other variable:
7A: 35x-21y=490
3B: 9x-21y=180
7A-3B: 26x=310, x=310/26=155/13.
SOLUTION x=155/13, y=-45/13
Check the solution by substituting x and y values into A and B.