Answer:
60 feet
Step-by-step explanation:
We know that a triangle has 3 sides, in this case we will call them a, b and c.
It tells us that everything is material, it measures 20, that is:
a + b + c = 20
They tell us that she wants to triple each side and to know how much material she would need in total. Then it would be:
border material need = 3 * a + 3 * b + 3 * c
common factor 3:
border material need = 3 * (a + b + c)
border material need = 3 * 20
border material need = 60
Which means that she needs a total of 60 feet of material.