so we assume that the speed of the current was constant
Speed=distance/time
Distance=60
trip down=60/3=20mph
trip up=60/30=2mph
the speed of the current is the avavarage of the diffarence of 2 and 20 so the diffirance is 18 avagage is 9 so 9mph=speed of current 9+x=20 x=11 so the speed of the boat in still water is 11mph
the speed of the current is 9mph