How to solve this question?
Look at the picture.
[tex]\tan\theta=\dfrac{5}{4}\\\\\tan\theta=\dfrac{10}{x}\to\dfrac{10}{x}=\dfrac{5}{4}[/tex]
cross multiply
[tex]5x=10\cdot4\\5x=40\ \ \ \ |:5\\x=8\ cm[/tex]
|QR| = 13cm + 8cm = 21 cm