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).

Let u = -968/171 + -1/171. What is the common denominator of u and -32/39?
39

Two letters picked without replacement from uuzzuuuuuuuuuzuu. Give prob of picking 1 u and 1 z.
13/40

Let z be 69/21 - 4/14. Solve 0*f + 3*f - 4 = 2*s, -z*f = 3*s - 24 for s.

4