Your equation should be 5 - r + 2 = 3.
Something that could be done is to tie a rope long enough to cross the river and send the two younger brothers across first, then have Mike pull the boat back across the river with the rope and him get in the boat and row it across the river with just himself and the gear.
Another option is you can unload some gear, put the boys in the boat, row them across the river, unload the two younger boys, go back for the rest of gear and load it into the boat then come back.
Hope this helps!
None of those are correct 630
