Question 77359
What you need for this is
time against current = time with current
or, the same thing,
(distance / rate upstream) = (distance / rate downstream)
Let c equal the rate of the current
{{{54 / (20 - c) = 66 / (20 + c)}}}
{{{20*66 - 66c = 20*54 + 54c}}}
{{{1320 - 66c = 1080 + 54c}}}
{{{120c = 240}}}
{{{c = 2}}} mi/hr answer