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 {e: 4, z: 1, r: 9}. What is prob of picking 3 r?
[A]: 3/13


[Q]: Let f(c) = 53*c + 6. Let p be f(3). What is the highest common divisor of p and 15?
[A]: 15


[Q]: What is 7/2 of a litre in millilitres?
[A]:
3500