The angles of triangle ABC are $\angle A = (x + 15)^\circ$, $\angle B = (2x - 10)^\circ$ and $\angle C = (3x + 25)^\circ$. What is $\angle B$?

Explanation

1. 01

   Angle sum: $(x + 15) + (2x - 10) + (3x + 25) = 180$.

2. 02

   $6x + 30 = 180$, so $x = 25$.

3. 03

   $\angle B = 2 \times 25 - 10 = 40^\circ$. ($\angle A$ is also 40° and $\angle C$ is 100°.)