A motorboat moves up a river at a speed of \(9 \mathrm{~m} / \mathrm{s}\) relative to the land. The river flows at a velocity of \(1.5 \mathrm{~m} / \mathrm{s}\). The boat is powered by a jet-propulsion unit which takes in water at the bow and discharges it beneath the surface at the stern. Measurements in the jet show its velocity relative to the boat to be \(18 \mathrm{~m} / \mathrm{s}\). For a flow rate through the unit of \(0.15 \mathrm{~m}^{3} / \mathrm{s}\), calculate the propulsive force produced.