Mr. Morris is going to save money and replace his sailboat's mainsail himself. He must determine the area of the mainsail in order to buy the correct amount of material. Calculate the area of the parallelogram to determine how much material should be purchased. Be sure to explain how to decompose this shape into rectangles and triangles. Describe their dimensions and show your work.

First of all, you have to consider the geometric shapes you could use in order to represent the mainsail. A sail is typically represented in the way of a rhombus, which makes sense considering they are telling you that you have to decompose the shape into rectangles and triangles.
Such triangle can have the following dimensions:
Triangle (Dimensions)
Base = 4ft
Height = 15ft
On the other hand, the rectangle can have the following dimensions:
Rectangle (Dimensions)
15 ft x 20ft
To get the area of the mainsail, you need to add up the sum of the areas of each individual part.
how to obtain these areas
Rectangle: 15x20 = 300ft²
Triangle #1: 1/2(4*5) = 30ft²
Triangle #2: 1/2(4*5) = 30ft²