hot air balloon weighing 30n is tied to the ground by a string to prevent from floating of the ground. the volume of the balloon is 20m^3 and the density of air is 1.3 kg kgm^-3.find force exerted by the rope on the balloon

The flame produced by the burner of a gas (propane) grill is a pale blue color when enough air mixes with the propane (c3h8) to burn it completely. for every gram of propane that flows through the burner, what volume of air is needed to burn it completely? assume that the temperature of the burner is 195.0°c, the pressure is 1.05 atm, and the mole fraction of o2 in air is 0.210.