A boat takes 4 hours longer to go 30 miles up the river than to return If the boat cruises at 10 miles per hour in still water what is the rate of the current?

if a boat cruises at 10 mph in still water, it can go 30 miles in 3 hours. if it takes the boat 7 hours to go that same 30 miles, it's speed must be 4.28 mph (30 mi / 7 hrs) which would make the current 5.71 mph