Wherever you choose to put your #60˚# angle, you have to remember that the length of its opposite side is #8.3m#.
I chose my #60˚# angle as being the angle opposite to the right angle, which means the remaining angle is #30˚#.
We know, #sin theta=y/h# (#y# being the opposite side of angle #theta# and #h# being the Hypotenuse)
#theta = 60˚#, #y=8.3m# and #h# is the unknown.
#sin theta=y/h=>sin60˚=8.3/h=>h=8.3/(sin60˚)=9.58m#
Another way to do this is to choose the #30˚# angle as the angle opposite to your right angle. Here you will use #cos30˚# instead of #sin60˚# because they said #8.3m# is the length of the side opposite the #60˚# angle and that means your #8.3m# is now #x# (the adjacent of #30˚#).
#cos theta=x/h=>cos30˚=8.3/h=>h=8.3/(cos30˚)=9.58m#
Note that cosine of #30˚# is the same as the sine of #60˚#. Realizing that is going to help you memorize the unit circle easily.
If you did not understand, please take a look at the picture.
Hope this helps :)
