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).

[Q]: Three letters picked without replacement from oxccztxcccocottcxxto. Give prob of picking 2 o and 1 t.
[A]: 2/95


[Q]: Four letters picked without replacement from {w: 2, k: 1, o: 1, a: 2, b: 2}. What is prob of picking 1 k, 2 a, and 1 b?
[A]: 1/35


[Q]: Let f(g) = g**2 - 2*g - 4. Let s be f(4). Suppose 119 - 31 = s*r. Let k = r - 15. What is the units digit of k?
[A]:
7