This graph has the hill and valley shape of a sine function, so $\displaystyle{y}={a}{\sin{{b}}}{x}\usepackage{cmbright}\Huge\$ . The amplitude is 4. It has the same orientation as the graph of $\displaystyle{y}={\sin{{x}}}\usepackage{cmbright}\Huge\$ and therefore $\displaystyle{a}={4}\usepackage{cmbright}\Huge\$ .

Now there are 3 cycles shown on the interval $\displaystyle{\left[{0},{3}\pi\right]}\usepackage{cmbright}\Huge\$ , or 2 cycles on the interval $\displaystyle{\left[{0},{2}\pi\right]}\usepackage{cmbright}\Huge\$ . This tells you that $\displaystyle{b}={2}\usepackage{cmbright}\Huge\$ . So this could be the graph of $\displaystyle{y}={4}{\sin{{2}}}{x}\usepackage{cmbright}\Huge\$ .