Question

8. In ΔRST, m∠R = (2x + 10)°, m∠S = (2x + 25)°, and m∠T = (x – 5)°.

Answer 1

The measures of the angles in a triangle add up to 180°.
$(2x+10)^\circ+(2x+25)^\circ+(x-5)^\circ=180^\circ \\ 2x+10+2x+25+x-5=180 \\ 5x+30=180 \\ 5x=180-30 \\ 5x=150 \\ x=\frac{150}{5} \\ \boxed{x=30}$

Answer 2

The sum of the measures of the interior angles of a triangle is $180^{\circ}$.

So,
$2x+10+2x+25+x-5=180\\ 5x=150\\ x=30$