We have to determine the empirical (frequentist) probability of each of the blood types.
We have a treatment with a total of 300 patients.
The outcome we get out of the experiment is:
- Blood type A: 63 positives out of 90.
- Blood type B: 31 positives out of 124.
- Blood type AB: 6 positives out of 6.
- Blood type O: 0 positives out of 80.
The probability for each group can be estimated as the ratio between the positive outcomes and the total of each blood type.
Blood type A:

Blood type B:

Blood type AB:

Blood type O:

Answer:
a) 0.70
b) 0.25
c) 1
d) 0