Answer
see graph.
Work Step by Step
Given $y=-\frac{1}{4}sin(\frac{3}{4}x+\frac{\pi}{8})=-\frac{1}{4}cos[\frac{3}{4}(x+\frac{\pi}{6})]$, we can identify its amplitude as $\frac{1}{4}$, period as $p=\frac{2\pi}{3/4}=\frac{8\pi}{3}$, and phase shift as $\frac{\pi}{6}$ to the left, see graph.
