You found the correct amplitude and orientation, but the period is incorrect. Perhaps you recognized that the period of the graph is 3 times the period of $\displaystyle{y}={\sin{{x}}}\usepackage{cmbright}\Huge\$ , and thought that would make $\displaystyle{b}={3}\usepackage{cmbright}\Huge\$ . But to find the value of

b, you must set the period equal to $\displaystyle\frac{{{2}\pi}}{{\left|{b}\right|}}\usepackage{cmbright}\Huge\$ . The correct answer is $\displaystyle{y}=-{4}{\sin{{\left(\frac{{1}}{{3}}{x}\right)}}}\usepackage{cmbright}\Huge\$ .