Question 77443
Perimeter of a triangle is the sum of the lengths of its sides. For example, if the three sides of a triangle are A, B and C, then the perimeter is A + B + C. 
In this case 3x+7, 4x-9, and 5x+6 are the 3 sides.

therefore Perimeter = 3x+7 + 4x-9 + 5x+6 
                    = 12x + 4.