Can someone help me with these 3 questions ASAP

Which equation represents the partial sum of the geometric series?

(05.02) 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.

Ay = 6, cy = 15, and yd = 4. what is the measure of by?