Chapter P, Prerequisites - Section P.9 - Modeling with Equations - P.9 Exercises - Page 73: 65

120 ft.

Let the length of the parcel be x. The diagonal of the parcel is then x + 10. Using the Pythagorean Theorem, we can set up an equation: $25^{2} + x^{2} = (x+10)^{2}$ $2500 + x^{2} = x^{2} + 20x + 100$ $2400 = 20x$ $x = 120$ Therefore, the length of the parcel is 120 ft.