Y= 3x+8
y= -2x - 7

how do i find the solution of the problem with the substition method?

Use one of the equation substitute for y

3x + 8 =-2x - 7
step 1 move the variable on one side
3x + 2x + 8 = -7
add the 3x + 2x = 5x
5x +8 = -7
subtract the 8 to both side
5x + 8 - 8 = -7 - 8
the (8-8) cancels out because it equal to zero
you are left with 5x = -15
divide the 5 on both sides and you get x = -3

in order to find your just plug in ×= -3 to any equation to find y.
I hope this helps