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]: Suppose 2*s - 2*z = 18, -4 = -2*s - z - 1. Suppose -v + 9 + 6 = -s*o, 17 = 3*v + 2*o. What is the units digit of v?
[EX A]: 7

[EX Q]: Let q = 14 - 24. Let z = q + 21. Solve -z = 2*c - 1 for c.
[EX A]: -5

[EX Q]: Four letters picked without replacement from {c: 2, f: 3, z: 4, a: 9}. What is prob of picking 3 f and 1 z?
[EX A]:
1/765