Probability of a Poisson Distribution without t given problem

#1
This is on my final exam study guide for statistics. I have absolutely no idea how to do it

Problem 1: Valerie Variance is taking her "no-time limit " final exam. As always, the exam has an infinite number of questions and the instructor gives no partial credit. Valerie being a diligent student attempts ALL problems. The number of problems that Valerie does CORRECTLY is described by a POISSON distribution with a mean of 8.0 She will PASS if she gets AT LEAST 8 problems correct. GIVEN that she gets AT MOST 11 problems correct, what is the probability that she passes the exam. (Use table for Poisson distribution for calculations) a) .8881 b) .5747 c) .4351 d) .6471 e) .4899

The answer should be e).4899 from the solution, but I have no idea how to get that.

All bookwork and homework gives the value of t. I've tried several ways and can't figure this out.
Any help is appreciated!