Please explain this graph and the answer, how to understand the answer? thanks

A firm employs a production function Q = F(K, L) for which only two values of K are possible, K1 and K2. Its ATC curve when K = K, is given by ATC1 = Q2 - 40 + 6. The corresponding curve for K = K2 is ATC2 = Q2 - 80 + 18. What is this firm's LAC curve? ANSWER: ATC curves are parabolas. The minimum points are dATC1 = 20 - 4 = 0, Q = 2. ATC, (2) = 22 - 4 x 2+6=2. do dATC2 = 20 - 8 = 0, Q = 4. ATC2(4) = 42 - 8 x 4+ 18 = 2. do Therefore, ATC2 curve is located to the right of ATC, (Q1