For this case what we should do is to see the problem as a rectangle triangle, where we have a side, an angle and we want to calculate the hypotenuse.
We then have the following trigonometric relationship:
sine (x) = (C.O) / (h)
Where,
x: angle
C.O: Opposite leg
h: hypotenuse
Substituting values:
sine (70) = (20) / (h)
Clearing h:
h = (20) / (sine (70))
h = 21.28 feet
Answer:
the ladder must be 21.28 feet long
