Answer
Please see the work below.
Work Step by Step
We know that
$\nu=\frac{E}{h}$
$\nu=\frac{7.1736\times 10^{-19}}{6.626\times 10^{-34}}=1.0826\times 10^{15}s^{-1}$
We also know that
$\lambda=\frac{c}{\nu}$
We plug in the known values to obtain:
$\lambda=\frac{2.998\times 10^8}{1.0826\times 10^{15}}=2.7691\times 10^{-7}m=276.91nm$