Answer:
15
Explanation:
In an equilateral triangle all the sides length are the same. Set two sides equal to each other and solve for x
3x + 6 = 6x - 3 Subtract 3x from both sides
6 = 3x -3 Add 3 to both sides
9 = 3x Divide each side by 3
3 = x
Now that we know x is 3, plug this into the expression for any side and find the side length
3x + 6
3(3) + 6
9 + 6 = 15