I’m guessing that x is the angle on the right that isn’t shown?
Anyways if that’s the case then:
We know that the sum of all the angles of a triangle add up to 180 degrees.
In this triangle we know that one angle is 55 degrees and the other is 90 degrees, so to find the last angle we do the sum of all the angles and we remove the 2 angles:
180- (55+90)= 35 degrees.
x= 35 degrees
