Chapter 8 - Applications of Trigonometric Functions - 8.5 Simple Harmonic Motion; Damped Motion; Combining Waves - 8.5 Assess Your Understanding - Page 553: 1

amplitude = $5$ periods = $\dfrac{\pi}{2}$

If a function has form $y=A\sin{(\alpha x)}$, then $|A|$ stands for the amplitude and $T =\frac{2\pi}{\omega}$ stands for the period. Hence, here we have amplitude:$|5|=5$ period: $\frac{2\pi}{4}=\frac{\pi}{2}$.