Answer:
C; D; B; B
Step-by-step explanation:
14) 1/((1/4) + (1/7)) = 1/(11/28) = 28/11 (C)
15) 1/((1/x) + (1/3x)) = 3--> (1/x) + (1/3x) = 1/3 --> 4/3x = 1/3 --> x = 4 (D)
16) 56 - 28 = 28 --> 28/(4*2) = 3.5 hours --> 56/3.5 = 16mph (when adding the stream's speed)--> 16mph - 4mph = 12mph (B)
17) 540 - 480 = 60 --> 60/(9*2) = 10/3 hours --> 540/(10/3) = 162 (when adding the current) --> 162mph - 9mph = 153mph (B)
