100%/x%=20/15
(100/X)*x=20/15*x --I multiply both sides of the equation by X
100=1.33333333333*x --I divided both sides of the equation by .........................................(1.33333333333) to get X
100/1.33333333333=x
75=x
x=75
15 is 75% of 20
Wait what did she have in her account? We need to know to answer.
The given MGF is that for a random variable following a Poisson distribution with parameter

.
This means

, and

has PMF

So, the desired probability is

This is equivalent to