Step 1:
Let $X$ be the random variable denoting the number of accidents involving taxi drivers in a year.
$X\sim P(3)$
$P(X=x)=\large\frac{e{-3}3^x}{x!}$
Step 2:
Probability that a taxi driver is not involved in any accident =$P(X=0)=e^{-3}=0.0498$
Out of 1000 drivers the expected number of drivers who will not be involved in any accident =$n\times probability$
$\Rightarrow 1000\times 0.0498=50$(approx)