What is the perimeter of a triangle with the given side lengths?
s1 = x – 3 ft
s2 = x + 2 ft
s3 = x + 4 ft

p= +

The perimeter of any shape is the distance all the way around it.

For a triangle, it's the sum of the three side lengths.

I would normally copy them into my answer and then add them up.
But you've set them up in such a beautiful table in the question,
you can just look at that list and add them up.

Add up all the x's :     x + x + x = 3x

Add up all the plain numbers:  -3 + 2 + 4 = 3

There's your perimeter . . . . .  3x + 3 .