Exponential and Logarithmic Functions · Hard problem

A solution has pH $4.5$, where $\mathrm{pH}=-\log[\mathrm{H}^{+}]$. Find $[\mathrm{H}^{+}]$. A second solution is $20$ times more acidic (its $[\mathrm{H}^{+}]$ is $20$ times larger); find its pH (round to two decimals).