In the figure shown the velocity of river current grows in proportion to the perpendicular distance from the bank and reaches its maximum ${\text{v}}_{\text{0}}\text{=9\hspace{0.17em}kmph,}$ in the middle. A boat is so moving in the river that its velocity v = 18 kmph relative to the water is constant and perpendicular to the direction of river flow. Assume the width of the river is d and boat starts from point O with reference to the above situation answer the following questions