The probability of no more than 4 typos on a page is closest to a. 0.938
How to solve the problem
We can solve this problem through the use of Microsoft excel. To solve this we would have to use this excel formula
POISSON.DIST(4, 2.1 , 1)
where 4 is the probability
2.1 is the mean
Hence
P(X ≤ 4 ) = POISSON.DIST(4, 2.1 , 1)
= 0.937873885
this is approximately
0.938
The excel output is added as an attachment