A straight tube, closed at one end and open at the other end, contains a stoichiometric CH4-air mixture at 300 K and 1 atm. The mixture is ignited at closed end, causing a planar deflagration to propagate down the tube toward the open end. Calculate the speed of the unburned gas relative to the tube wall. Assume that the gas density decreases by a factor of 7 as a result of combustion and that viscous effects are negligible. The laminar flame speed is SL = 44 cm/s.