The graph does have the shape of a sine function, and you found the correct amplitude, but the period is incorrect. Perhaps you recognized that the period of the graph is one fourth the period of $\displaystyle{y}={\sin{{x}}}\usepackage{cmbright}\Huge\$ , and thought that would make $\displaystyle{b}=\frac{{1}}{{4}}\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\$ .