The perimeter of the top of a desk is 54 inches if the length of the desk is 15 inches what is the width of the desk

54-15=39
if you want to check your answer you add 39+15=54

The formula for perimeter is P=2l+2w where P is perimeter, l is length and w is width. P=54 inches and l is 15 inches but we do not know the value of w. Let's replace the letters with their number
P=2l+2w
54=2(15)+2w
54=30+2w  let's group like terms or numbers that are similar. 54 and 30 have no letters attached to them and so are the similar. So let's move 30 to the right side. Since 30 is positive on the right side, subtract it from both sides of the equation.
54-30=30+2x-30
24=2w
24/2=2w/2
12=w Therefore the width is 12 inches.

Here, feel free to ask if there are any questions