Chapter 7 - Section 7.6 - Proportions and Problem Solving with Rational Equations - Exercise Set - Page 541: 63

5.25 hours

experienced: 6 hours (1/6 done in an hour) second cook: 7 hours (1/7 done in an hour) $1/6 + 1/7 + 1/x = 1/2$ $42(1/6 + 1/7 + 1/x = 1/2)$ $7 + 6 + 42/x = 21$ $13 + 42/x = 21$ $42/x = 8$ $42/x*x = 8*x$ $42 = 8x$ $42/8 = 8x/8$ $21/4 = x$ $x = 5.25$