You'll first need to calculate the measure of angle R. From the diagram we see that
opp 33
tan R = ------- = ----- = 0.589, so, using the inv. tang. function, R = 0.589 rad.
adj 56
opp 33
Then sin R = --------- = sin 0.589 rad = ------------------------- = 0.508 rad
hyp sqrt(33^2 + 56^2)
or 29.089 degrees
