Given a simple high-school level math question, you are required to solve it and provide the final answer. The final answer is always a single number. These questions can range from a variety of topics like simple arithmetic, solving equations, converting a quantity from one unit to another, finding remainders/GCD/LCM, finding probabilities etc. Each question has only one correct answer. This answer can be a positive or negative integer, a fraction or a decimal number. If the answer is a negative number use the hyphen (e.g. -42) symbol for the minus sign. For decimal numbers, do not add extra zeros after the decimal point. For fractional numbers, separate the numerator and denominator using a forward slash (e.g. 3/25).

[EX Q]: Four letters picked without replacement from rsisririrsshs. What is prob of sequence iirr?
[EX A]: 3/715

[EX Q]: Let a(c) = -c**3 - 13*c**2 - 23*c - 5. Let s be a(-11). Calculate the highest common factor of s and 30.
[EX A]: 6

[EX Q]: Find the common denominator of (-9)/(-24) + (-30)/(-24) and 5/4.
[EX A]:
8