Question 530140
The apparent speed is 9mph with the current and 3 mph against the current.
The average is the speed of the boat in still water (6mph) and the difference is the speed of the current (3mph).
However, the intention of the problem must have been to set and solve a system of equations, so let's get silly.
Let {{{b}}} be the speed of the boat in still water in mph, and
{{{r}}} be the speed of the current in mph.
We could say that the total speed going downstream, in mph, is
{{{b+r=9}}}
and that the total speed for the return trip, in mph, is
{{{b-r=3}}}
Then we solve the system of equations.
We could do it by substitution, solving for {{{b}}}
in the second equation {{{b=r+3}}}
and substituting that into the first equation to get
{{{(r+3)+3=9}}} so {{{r+6=9}}}, so {{{r=9-6}}} so {{{r=3}}}
Then we substitute that solution in
{{{b=r+3}}} and find {{{b=3+3}}} so {{{b=6}}}
We could also solve by other methods, but it's Friday night and I have other stuff to do.