A piston cylinder arrangement has an impeller protruding through the wall so that mechanical work can be done on the system. The piston weighs 15 lbf and is a circular disk with a diameter of 4 inches. The cylinder contains 1lbm of air initially at 537R that is heated to 640R by 17 Btu heat addition and shaft work. If the change in internal energy for the air is 25 Btu/lbm, how much shaft work was done by the impeller? Note: the air obeys the relation that pV=mRiT. Note: the MW of air can be assumed to be 29 lbm/lbmole and the specific gas constant for air is Ri = 53.34 ft lbf/lbmR