4. Opportunity cost. Richardses' Tree Farm, Inc. has branched into gardening over the years and is now considering adding patio furniture to its product lineup. Currently, the area where the patio furniture is to be displayed is a vacant slab of concrete attached to the indoor shop. The company originally paid $8,500 to put in the slab of concrete three years ago. It would now cost $12,000 to put in the same slab of concrete. Should the company consider the concrete slab when expanding its outdoor garden shop to include patio furniture? If yes, which value should it use