5x - 42 = y
x + y = 18
To find the variables numeric value, you can do substitution and plug in the equation of y(first equation) into the second equation because y is already by itself.
x + (5x - 42) = 18
x + 5x - 42 = 18
6x - 42 = 18
Add 42 on both sides
6x = 60
Divide 6 on both sides to get x by itself
x = 10
Now that you know "x", you can plug it into either of the equations to find "y"
x + y = 18
10 + y = 18
y = 8
5x - 42 = y
5(10) - 42 = y
50 - 42 = y
8 = y
x = 10, y = 8
