Question 1208940
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c = speed of the current in mph


Going against the current (i.e. upstream) the boat's speed goes from 16 mph to 16-c mph.
distance = rate*time
d = r*t
d = (16-c)*(20/60)
d = (1/3)(16-c)


Going with the current (downstream) means the boat goes from 16 mph to 16+c mph.
d = r*t
d = (16+c)*(15/60)
d = (1/4)(16+c)


The two equations involve the same distance. 
This allows us to equate the right hand sides to solve for c.
(1/3)(16-c) = (1/4)(16+c)
12*(1/3)(16-c) = 12*(1/4)(16+c)
4(16-c) = 3(16+c)
64-4c = 48+3c
64-48 = 3c+4c
16 = 7c
c = 16/7
c = 2.2857 mph approximately


Side notes: <ul><li>To convert from mph to miles per minute, divide by 60.</li><li>The improper fraction 16/7 converts to the mixed number 2 & 2/7</li></ul></font>