Answer
At half the speed of light, v/c = 1/2, measurements of time intervals differ by a factor 1.15.
At $99.5\%$ of the speed of light, v/c = 0.995, measurements of time intervals differ by a factor of 10.
Work Step by Step
$$\gamma = \frac{1}{\sqrt{1-0.5^{2}}} = 1.15$$
$$\gamma = \frac{1}{\sqrt{1-0.995^{2}}} = 10.0$$
This is discussed on page 666.