Answer
(a) $4.0\times10^{2}\,nm$
(b) $5.0\times10^{-19}\,J$
Work Step by Step
(a) $c=\nu\lambda$ where $c$ is the speed of light, $\nu$ is the frequency and $\lambda$ is the wavelength.
$\implies \lambda=\frac{c}{\nu}=\frac{3.00\times10^{8}\,m/s}{7.5\times10^{14}\,s^{-1}}=4.0\times10^{-7}\,m$
$=4.0\times10^{2}\times10^{-9}\,m=4.0\times10^{2}\,nm$
(b) Energy $E=h\nu=(6.626\times10^{-34}\,J\cdot s)(7.5\times10^{14}\,s^{-1})$
$=5.0\times10^{-19}\,J$
