Adding and Subtracting Polynomials

The perimeter of a trapezoid is 39a – 7. Three sides have the following lengths: 9a, 5a + 1, and 17a – 6. What is the length of the fourth side? (1 point)
12
a – 7
8a – 2
31a – 5

Question

Adding and Subtracting Polynomials

 The perimeter of a trapezoid is 39a – 7. Three sides have the following lengths: 9a, 5a + 1, and 17a – 6. What is the length of the fourth side?  (1 point)
12
a – 7
8a – 2
31a – 5

anonymous · Answer

What am I supposed 2 do?

whpalmer4 · Answer

Well, you know that the perimeter is the sum of the 4 sides.  You know three of the sides, and you know the perimeter.  The fourth side must be the perimeter - (sum of the three known sides).  Write the equation that reflects that, then solve it.