Answer:
74 Km/h
Explanation:
For boat A:
1 = 2l/v_1
 =2×74/74  h
 =2h
where = 74 wide of the lake, 1- speed of boat A
For boat B:
2 = l/v_21 Â + l/v_22 Â Â
  = 74/37  + 74/111 ℎ
  = 2.66 ℎ
where v_21= 37 /ℎ and v_22 = 111 /ℎ speeds of boat B
boat A completes the round trip first. The difference of times equals:
                        ∆ = 2 − 1
                           =2.66 ℎ − 2ℎ
                           =0.66 ℎ or 40 n
boat A, ∆ = 40 n
c) Average speed for boat A equals:
                        V = 2 /1
                           =148/2 Km/h
                           =74 Km/h