Tell which equation you would use to isolate a variable in order to solve the system using substitution. explain your reasoning.

2x + y=-10
3x-y=0

2x+y=-10
Multiply both side by 3
2x*3+y*3=-10*3
6x+3y=-30

3x-y=0
Multiply both side by 2
3x*2-y*2=0*2
6x-2y=0
Next, use substitute property
6x+3y=-30
    -
6x-2y=0
    =
y=-30
3x-y=0
Substitute y with -30
3x-30=0
Add 30 to each side
3x-30+30=0+30
3x=30
Divided both side by 3
3x/3=30/3
x=10, so the solution pair is (10,-30). In this case, there is the first way to solve these two equation.
Then, I would use equation 3x+1.5y=-15 in this question by multiply 2x+y=-10 by multiplying both side by 3/2 to eliminate x and to solve variables for y. Hope it help!