\(V_d = V_b + V_c\)
\(\frac{distance}{time} = V_b + V_c\)
\(\frac{20}{1\frac{1}{3}} = V_b + V_c\)
\(15 = V_b + V_c\)
\( V_b = 15 - V_c\)
\(V_u = V_b - V_c\)
\(\frac{distance}{time} = V_b - V_c\)
\(\frac{20}{2\frac{2}{9}} = V_b - V_c\)
\(V_b = 9 + V_c\)
\(15-V_c = 9 +V_c\)
\(V_c = 3\)
\(V_b = 9 + 3 = 12\)
Thus the rate of the boat on still water is 12 mph and the current is 3 mph