Answer:
31x^2-13x
Step-by-step explanation:
to find the perimeter of a triangle, add all sides.
P=a+b+c
P=(5x^2+x)+(8x^2-3x)+(18x^2-11x)
combine like terms
5x^2+8x^2-18x^2= 31x^2
x-3x-11x= -13x
