Answer :
Answer is 30°.
Triangle Sum Theorem:
This theorem states that sum of all angles in a triangle is equal to 180°.
Ex: In triangle ABC, then ∠A + ∠B + ∠C = 180°.
Here, (Given)
∠A = 90°
∠B = X (let's assume)
∠C = 60°
=> ∠A + ∠B + ∠C = 180°
=> 90° + X + 60° = 180°
=> X = 180° - 60° - 90°
=> X = 30°.
Learn more about Triangle sum Theorem here: https://brainly.com/question/18533481?referrer=searchResults
#SPJ2