Area of the parallelogram

the main mast of a fishing boat is supported by a sturdy rope that extends from the top of the mast to the deck. if the mast is 20 feet tall and the rope attaches to the deck 15 feet away from the base of the mast, how long is the rope?

for your diagram:

draw a sailboat with the sail a right triangle.

label the height 20 feet and the "bottom" 15 feet.

then solve for c (the oblique line).