im helping my brother with his homework but i completely forgot how to do this?

Question

Solve the system by substitution:

y=3x-4

x+5y=-4

Answer 1

x+5y=-4

y=3x-4

x+5*(3x-4)=-4
x+15x-20=-4
16x=-4+20
16x=16 Divide wth 16

x=1

y=3x-4
y=3*1-4
y=3-4=-1

x=1 y=-1

Cheking of result:
y=3x-4
-1=3*1-4
-1=3-4
-1=-1

x+5y=-4
1+5*(-1)=-4
1-5=-4
-4=-4