Help and please explain

So the right angle is equal to 90° and the rest is unknown.

using the triangle sim theorem, which states that all interior angles are equal to 180°.

so it would be x+2x+90°=180°.

then you would need to simply which is 3x+90°=180°

subtract 90° from both sides and get 3x=90°

and then divide both sides by 3 which is 30°

then you would need to find the angle of B which is 2x so you would need to substitute 30° for x which is 60°

the answer is 60°