The sum of n independent Poisson random variables each with parameter is itself a Poisson random variable with parameter .

So X is Poisson random variable with parameter 60*n = 60*100 = 6000. Therefore, X has a mean a 6000 and a variance of 6000.

Since n is fairly large, is approximately by the central limit theorem

so find

If you were dealing with a strict inequality, the answer would be different.