Answer:
C 9x^2 +15x +36
Explanation:
Equilateral triangles have the same angles and the same length sides.
All the sides of the triangle have the length 3x^2+5x+12
The perimeter will be 3s since the sides are the same
P=3s
P =3(3x^2+5x+12)
Distribute
P = 9x^2 +15x +36