Since this is a right triangle with 3 given sides, the longest must be the hypotenuse, and the other two sides are the legs.
The legs must be perpendicular to each other, so they define the base and the height of the triangle. It does not matter which leg you call the height: you will get the same area.
(1/2) base times height equals the area of any triangle, and that is (1/2) * 30 * 16 = 240 square centimeters.
You could also use Heron's formula since you were given the lengths of all 3 sides, but that requires a lot more arithmetic. However, if this were not a right triangle, that would be the method of choice.
