A fire truck attaches two fire hoses to a hydrant to fight a fire. Each hose has a diameter of 20 cm. The underground water pipe going to the hydrant has a diameter of 100 cm. In the underground pipe, the water has a speed of 2.0 m/s. (a) How many kilograms of water are put on the fire in 30 minutes? (b) What is the speed of the water in the fire hoses?