Question

The sum of the measures of angle X and angle Y is 90. If the measure of angle X is 30 less than twice the measure of angle Y, what is the measure of angle X?

Answer 1

x + y = 90
x = 2y - 30

now sub 2y - 30 in for x in the first equation and solve for y

Answer 2

then you can sub that answer in for y in either of the equations to find x.
It is simple substitution.