USE LINEAR COMBINATIONS TO SOLVE THE SYSTEM OF LINEAR EQUATIONS (please show steps)

Question

1) -X+8Y=16 2) 4X+5Y=-2 3)4Y=15-3X
3X+4Y=36 5X-4Y=-23 2Y=3X+21

Answer 1

I will do one. Then, I will happily critique your thinking on others. Take the third.

4y=15-3x
2y=3x+21

double the second one..

4y=15-3x
4y=6x+42

subtract, then the result is ..
0=9x-45 and solve for x.