hydraulics assignment, one exercise

I need this problem solve, all the working out included please.

Three conduits will be designed, both feed joint C (as shown in the picture). From containers A and B the water is led to point D. The length of the pipes and the height of each point is shown in the picture as well. Point A must supply 20 lt/seg, point B 10 lt/seg. In point D the piezometric head should not descend below 230 meters high (20 meters above the ground).

We need to find the diameters for the pipes (L1, L2 and L3), there are 4 commercial sizes to choose, 76, 102, 155 y 203 mm, also we are trying to find the cheapest way. The material of the pipes is cast iron, over time the absolute rugosity of this material can increase up to 25%.