Explanation:
y = 3x + 14
y = -4x
substitution means that we use the information of one equation in the other equation to reduce it to one equation in one variable. with the solution of that we go into the other equation and solve for the second variable.
in our case we use the second equation directly in the first and get
-4x = 3x + 14
-7x = 14
x = -2
and now, with this x = -2 we go to the second equation
y = -4×-2 = 8