Question 121626
{{{s = 4}}}mi/hr = speed of stream
{{{b}}} = speed of boat in still water
{{{2 / (b - s) = 10 / (b + s)}}}
{{{2 / (b - 4) = 10 / (b + 4)}}}
multiply both sides by {{{(b - 4)(b + 4)}}}
{{{2(b + 4) = 10(b - 4)}}}
{{{2b + 8 = 10b - 40}}}
{{{8b = 48}}}
{{{b = 6}}}mi/hr