The formula t= + gives the
total time t (in hours) needed for a
boat to travel upstream a distance
of d miles and then back
downstream the same distance,
where b is the speed of the boat in
still water and c is the speed of the
river's current (both in miles per
hour). How can you write a formula
that gives the speed of the current
in terms of the other variable? What
is the formula? (3 points)