Answer:
 0.5588
Step-by-step explanation:
The CDF of an exponential function with mean μ is ...
 CDF(x) = 1 - e^(-x/μ)
Then the probability that graduation will occur in 4.5 years or less is ...
 P(x<4.5) = 1 - e^(-4.5/5.5) ≈ 0.558767 ≈ 0.5588