If a deck is 18 ft long by 10 ft wide what is the linear feet?

Hmmmm, the answer depends on what you mean by "what is the linear feet?". Linear feet is a straight measurement, which in this case is 18 ft long by 10 ft wide. If you are trying to find the perimeter (the distance around the deck) add the length and the width and multiply by 2: (18 + 10)x2 = 56 ft around. If what you want is the area (the space of the surface of the deck), multiply the length by the width: 18 x 10 = 180 sq ft.