A river flows at a speed vr = 5.88 km/hr with respect to the shoreline. A boat needs to go perpendicular to the shoreline to reach a pier on the river’s other side. To do so, the boat heads upstream at an angle θ = 31◦ from the direction to the boat’s pier. Find the ratio of vb to vr, where vr is defined above and vb is the boat’s speed with respect to the water.

Working alone at its constant rate, pump x pumped out ¼ of the water in a tank in 2 hours. then pumps y and z started working and the three pumps, working simultaneously at their respective constant rates, pumped out the rest of the water in 3 hours. if pump y, working alone at its constant rate, would have taken 18 hours to pump out the rest of the water, how many hours would it have taken pump z, working alone at its constant rate, to pump out all of the water that was pumped out of the tank? a) 6b) 12c) 15d) 18e) 24