Chapter 7 - Section 7.6 - Proportions and Problem Solving with Rational Equations - Exercise Set - Page 539: 43

217 mph

with wind: $630 = (x+35)*t$ against wind: $455 = (x-35)*t$ $630 = (x+35)*t$ $630/(x+35) = (x+35)*t/(x+35)$ $630/(x+35) = t$ $455 = (x-35)*t$ $455/(x-35) = (x-35)*t/(x-35)$ $455/(x-35) = t$ $630/(x+35) =455/(x-35)$ $455*(x+35) = 630*(x-35)$ $455x +15925 = 630x-22050$ $15925 = 175x-22050$ $37975 = 175x$ $37975/175 = 175x/175$ $x = 217$