Math question geometry

the triangle PQR is right-angled.
PQ= 20cm and the hypotenuse PR= 40 cm
what is the angle at R?
answer key= 30 degrees
I thought as long as this is a right-angled triangle, the answer should be 45 degrees. can someone help?

a right angled triangle has the angles 45°-90°-45° only if it is also isosceles, otherwise the angles can be bigger or smaller
sin(R) = opposite/hypothenuse = 20/40 = 1/2
and sin(30°)=1/2 so R=30°