30, 60, 90 degree angles of a triangle. Opposite sides
The answer by Sydur R. is correct. However, another key in this problem is to figure out the kind of triangle you have. What is also important is that an altitude is always perpendicular to the opposite side giving you a right angle (Pythagorean theorem) to work with. This might help you.
Equilateral = length of side * (√3)/2
Right = (length of side a * length of side b) / length of side c