By the traingle sum theorem, the sum of the angles in a triangle is 180°. Therefore, using the given and triangle sum theorem, m(∡P) + m(∡Q) + m(∡R) = 180°.
(5x)° + (5x)° + (8x)° = 180°. Simplifying the equation gets 18x=180°. Finally, using the division property of equality, x=10°.