The cost (in dollars) of making n feet of cabinet is represented by C = 18n + 45

The equation you have represents the cost for n feet of cabinet. If you know what the cost is C, you can solve for n.

The cost is given as $441. Plug into equation.

441 = 18n + 45

Subtract 45 from both sides

396 = 18n

Divide by 18 to get n

22 = n

The answer is 22 feet of cabinet.