Find the area of the largest rectangle that can be inscribed in a right triangle with legs of lengths 3 cm and 4 cm if two sides of the rectangle lie along the legs.

I drew a picture and i know I'm trying to maximize the area so i need to use the area formula, but I'm not really sure where to start, not sure how the 4 and 3 cm are related to the rectangle other than the fact it cannot have length or widths greater than those.

Any help would be greatly appreciated