Chapter 1 - Equations and Inequalities - 1.6 Other Types of Equations and Applications - 1.6 Exercises - Page 147: 39

$78\ hours$

Step 1. Use the table given in the exercise, the rate from B would be $\frac{1}{2x}$ and the part of job completed from B would be $26(\frac{1}{2x})$. Step 2. Together, the total parts should be 1, we have $26(\frac{1}{x})+26(\frac{1}{2x})=1$ or $\frac{1}{x}+\frac{1}{2x}=\frac{1}{26}$ Step 3. Solve the above equation: $\frac{3}{2x}=\frac{1}{26}$, thus $x=39\ hrs$ Step 4. It takes B $2\times39=78\ hours$ alone.