What is the solution to the system of equations? use the substitution method to solve.

6=−4x+y
−5x−y=21

! and, if you don't mind, could you explain to me what the substitution method is? guys!

In the substitution method, you will take the value of one variable in one equation and replace the variable in the second equation with that value.
For instance
6=-4x+y
6+4x=-4x+y+4x              So the value of y is 6+4x
6+4x=y y=6+4x     
In the second equation, replace every y with 6+4x
-5x-y=21                        -9x-6+6=21+6                       x=-3    
 -5x-(6+4x)=21                  -9x=27             So using the value of y, we found -5x-6-4x=21                   -9x/-9=27/-9    the value of x

y=6+4(-3)  y=6-12  y=-6 Using substitution, we know that x=-3 and y=-6