Perform the operation indicated, then place the answer in the proper location on the grid. The perimeter of a triangle is 7a - 11b. If two of its sides are 2a + b and a - 9b, what is the third side?

Answer: 4 a - 3 b

Step-by-step explanation:

Since, the perimeter of the triangle = sum of all the three side of the triangle.

Here, two sides of the triangle are 2a + b and a - 9b,

And, the perimeter of the triangle = 7 a - 11

Let third side = x

Therefore, 2 a + b + a - 9 b + x = 7 a - 11 b

⇒ 3 a - 8 b + x = 7 a - 11 b

⇒ x = 7 a - 11 b - 3 a + 8 b

⇒ x = 4 a - 3 b (by operating like terms)