Chapter 4 - Section 4.5 - Graphs of Sine and Cosine Functions - Exercise Set - Page 595: 15

Please see below.

Please note that a sine function $y=A\sin Bx$ has amplitude $|A|$ and period $\frac{2\pi }{B}$. So the function $y=-\sin \frac{2}{3} x$ has amplitude $|-1|=1$ and period $\frac{2\pi }{\frac{2}{3} }=3\pi$.