Answer
$1.1\times 10^2\space yr$
Work Step by Step
We can determine the required time as follows:
As given that the world's total petroleum estimated reserves are $2.0\times 10^{22} J$ and yearly consumption is $1.8\times 10^{20}\frac{J}{yr}$
$\implies t=2.0\times 10^{22}J\times \frac{1 yr}{1.8\times 10^{20}J}$
This simplifies to:
$t=1.1\times 10^2\space yr$
