Answer:
The width of the desk is 12 inches.
Explanation:
Given:
The perimeter of the top of a desk is 54 inches.
The length of the desk is 15 inches.
Now, to find the width of the desk.
Let the width of the desk be
.
Putting the formula of perimeter to get the width:

⇒

⇒

Subtracting both sides by 30 we get:
⇒

Dividing both sides by 2 we get:
⇒

⇒

Therefore, the width of the desk is 12 inches.