Chapter 7 - Section 7.6 - Proportions and Problem Solving with Rational Equations - Exercise Set - Page 540: 48

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$6 = (x-3)*t$ upstream $10 = (x+3)*t$ downstream $6 = (x-3)*t$ $6/(x-3) = (x-3)*t/(x-3)$ $6/(x-3) =t$ $10 = (x+3)*t$ $10/(x+3) = (x+3)*t/(x+3)$ $10/(x+3) = t$ $6/(x-3) = 10/(x+3)$ $10(x-3) = 6(x+3)$ $10x-30 = 6x+18$ $4x-30=18$ $4x = 48$ $4x/4 = 48/4$ $x=12$