You have the following system of equations:
-10x - 4y = -18
x = y
In order to solve the previous equation, replace x = y into the first equation, and solve for y, just as follow:
.10(y) - 4y = -18
-10y - 4y = -18 simplify left side
-14y = -18 divide by -14 both sides
y = 18/14
consider x = y:
x = y = 18/14