1. I am in a boat with my son and we are carrying a rock. The boat is moving forward at 8knots. I weigh 170 #, my son weighs 70

#, the boat weighs 40 # and the rock weighs 30 #.While in motion, we throw the rock off the back of the boat with a velocity of 20 mph.How fast are we going (sans rock)?Note: Express speed in terms of mph and knots (typical unit of measure on water).