An Airplane Flew For 8 Hours At An Airspeed Of X Miles Per Hour And For 7 More Hours At 325 Mph. If The Average Airspeed For The Entire Flight Was 350 Mph, What Does X Equal?

The total distance traveled was
(350 mi/hr)(8 hr + 7 hr) = (325 mi/hr)(7 hr) + (x mi/hr)(8 hr)
350*15 = 325*7 + 8x (divide out units of miles)
(350*15 - 325*7)/8 = x (subtract 325*7 from both sides, then divide both sides by 8)
(5250 - 2275)/8 = x (evaluate)
2975/8 = x

x mi/hr = 371 7/8 mph