The length and a quarter of the width of a rectangle add up to 7 in, while the length and the width add up to 10 in. what are the rectangle's length and width?

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?