Answer:
x = 31
Explanation:
Exterior Angle Theorem
The exterior angle theorem states that when a triangle's side is extended, the resultant exterior angle formed is equal to the sum of the measures of the two opposite interior angles of the triangle.
In this particular triangle, the angle with measurement 121° is the exterior angle
The two interior angles are x and the one which is 90°
Therefore by the exterior angle theorem,
90° + x° = 121°
Subtract 90 from both sides
x = 121 - 90
giving
x = 31