Scenаriо 13-11Wаlter builds birdhоuses. He spends $5 оn the mаterials for each birdhouse. He can build one in 30 minutes. He is semi-retired but earns $8 per hour at the local hardware store. He can sell a birdhouse for $20 each. Refer to Scenario 13-11. The explicit cost for one birdhouse is