The perimeter of triangle abc is 54. the triangle has side lengths ab =3×,bc=4×,and ac=5× find the length of each side

Firstly setup an equation to find the perimeter:

3x + 4x + 5x = 54, this is because perimeter is equal to sum of all side lengths

Then combine like terms:
12x = 54

Now use the division property of equality by dividing both sides by 12:
x = 4.5

So then, you will substitute the value of x for each value of the side lengths: 
3(4.5) = 13.5 for AB, 4(4.5) = 18 for BC, and 5(4.5) = 22.5 for AC. 

Hope this helps and let me know if you have any more questions!