All 3 sides of an equilateral triangle are the same.
Set up an equation with two sides equaling each other and solve for n:
2n +15/4 = 7n
Subtract 2n from both sides:
15/4 = 5n
Divide both sides by 5:
n = (15/4) / 5
n = 3/4
Now you have a value for n, replace n and solve for the length:
7n = 7(3/4) = 21/4 = 5 1/4
Each side is 5 1/4
