Answer: a) 15:26, and b) 15:11.
Explanation:
Since we have given that
Number of graded tests = 15
Number of total tests = 26
Number of ungraded tests is given by

a) Proportion of all exams has Dr. Fitxgerald graded is given by
15:26.
b) Ratio of graded to ungraded tests is given by 15:11
Hence, a) 15:26, and b) 15:11.