Hey there!
To use the substitution method in order to solve the system of equations,
y=7x+8
y=x+20 , first notice that both equations are set equal to the same value, y.
Knowing this, 7x+8 and x+20 both equal the same value so you would set them equal to one another:
7x+8=x+20.
This would be substitution as you are substituting one of the equations in place of y.
Now, solve for x:
7x+8=x+20
6x+8=20
6x=12
x=2
Now that you know x equals the value of 2, you can substitute the value into one of the equations to find y:
y=x+20
y=2+20
y=22
Now that you have x=2 and y=22, you can conclude that your answer would be (2,22) or choice B.
Hope this helps and have a wonderful day! :)