A jet-propelled airplane with a mass of 9.6 Mg is flying horizontally at a constant speed of 1030 km/h under the action of the engine thrust T and the equal and opposite air resistance R. The pilot ignites two rocket-assist units, each of which develops a forward thrust T0 of 7.8 kN for 9.7 s. If the velocity of the airplane in its horizontal flight is 1085 km/h at the end of the 9.7 s, calculate the time-average increase in air resistance. The mass of the rocket fuel used is negligible compared with that of the airplane.