An equilateral triangle has sides of length s. if each side is increased by 15, represent the new perimeter in terms of s.

We know that an equilateral triangle has all sides equal.
Initial perimeter = s + s + s = s
Each side has been increases by  then the new perimeter is:

(s+15) + (s+15) + (s+15) = 3s + 45

So the new perimeter = 3s + 45

You need to show the box plots