Respuesta :

cedarwood79
Okie doke! So, the total perimeter is 10x + 2. So far, the combined sides of 5x and 2x + 9 is 7x + 9. So, when we look at our numbers and do some mental math, we'll see that we need 3x and we need to subtract 7. The length of the 3rd side is 3x - 7.