Question

Solving systems by substitution
y=-4x-7
-4x-y=7​

Answer 1

the variable y is given.
now, substitute y in the second equation to get
-4x - (-4x-7) = 7
then we solve

first distribute
-4x+4x+7=7
combine like terms
0+7 = 7
7 = 7

because the answer is true, the solution to this system is “all real numbers”