The sum of the measures of angle x and y is 90. if the measures of angle x is 30 less than twice the measures of angle y what is the measure of angle x?

First set up your two equations:

x + y = 90

x = 2y - 30

Then substitute what x equals in the second equation into the first equation:

(2y -30) + y = 90

Now solve for y:

3y -30 = 90
3y = 120
y = 40

Then use y = 40 and substitute the value for y into one of your original equations and solve for x.  I'll choose the first one, but either one will work.

x+ 40 = 90
x = 50

So your solution is x = 50 and y = 40