Triangles
Area = (1/2) x base x height. Pythagorean theorem: a^2 + b^2 = c^2 for a right triangle. With legs 6 and 8, c^2 = 36 + 64 = 100, so c = 10 and the area is (1/2)(6)(8) = 24. The three interior angles always sum to 180 degrees, which is what lets you find a missing angle from the other two.