The perimeter of triangle ABC is 36 cm. Its sides are proportional to the numbers 3, 4 and 5. Find the sides of the triangle.

Answer:
3x+4x+5x=36
12x=36
x=36/12
x=3
3x=3 into 3=9
4x=4 into 3=12
5x=5 into 3=15