A powerplant is situated at an altitude of 1000 ft above sea level. Flue gases enter the slack at 285 degree F and leave at 230 degree F. (a) Find the height of stack, in feet, necessary for a driving pressure of 0.1 psia if the outside air is at 50 degree F and (b) the percent change in gas flow if the outside air temperature changes m 60 degree F.