Answer
10.0 L of that $NaCl$ solution contains 15.0 moles of $NaCl$.
Work Step by Step
1. Since the molarity of that solution is equal to $ 1.50 \space M \space NaCl$:
$1 \space L \space solution = 1.50 \space moles \space NaCl$
$\frac{1 \space L \space solution}{ 1.50 \space moles \space NaCl} $ and $\frac{ 1.50 \space moles \space NaCl}{1 \space L \space solution}$
2. Use the conversion factors to calculate the volume of that solution that has 15.0 moles $NaCl$:
$15.0 \space moles \space NaCl \times \frac{1 \space L \space solution}{1.50 \space moles \space NaCl} = 10.0 \space L \space solution$
