The amplitude of $\displaystyle{y}={a}{\sin{{b}}}{x}\usepackage{cmbright}\Huge\$ is given by $\displaystyle{\left|{a}\right|}\usepackage{cmbright}\Huge\$ , so the amplitude of $\displaystyle{y}={3}{\sin{{\left(-{2}{x}\right)}}}\usepackage{cmbright}\Huge\$ is 3. The period equals

$\displaystyle\frac{{{2}\pi}}{{\left|{b}\right|}}=\frac{{{2}\pi}}{{\left|-{2}\right|}}=\frac{{{2}\pi}}{{2}}=\pi\usepackage{cmbright}\Huge\$ .