Let x be the speed of plane at no wind", in miles per hour (mph). Then the speed with the wind is (x+30) mph, the speed against the wind is (x-30) mph. Then the "time equation" is+ = 1.3 hours. ======================================> 60*(x+30) + 60*(x-30) = 1.3*(x^2-900) ====> 120x = 1.3x^2 - 1.3*900 ====> 1.3x^2 - 120x - 1.3*900 = 0 ====> = = . Only positive root makes sense x = = 101.2. Answer. The speed of the plane "at no wind" is 101.2 miles per hour.