Question 970625
Angles of a triangle add to 180 degrees.

So
180=x + (x-10) +90  =  2x -10 +90 =  2x +80

subtract 80 from each side

100= 2x

x=50 degrees

x-10=40  degrees

50 +40= 90
The right angle is 90
90 deg + 90 deg =180 deg

check