In triangle ABC, the angle A is 54 degrees, and the angle c is 15 degrees less. find the angle B of the triangle ABC.

Let’s use the theorem: The sum of the angles of a triangle is 180 degrees. Let’s find the angle С, because we know that it is 15 degrees less than the angle A = 54 degrees, then the angle C = 54 – 15 = 39 (degrees).
To find the angle B, you need to subtract the sum of the angles A and C from 180 degrees.
Find the angle B = 180 – (54 + 39) = 180 – 93 = 87 (degrees).
Answer. 87 degrees.