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]: What is prob of picking 3 h and 1 t when four letters picked without replacement from {h: 6, n: 4, t: 5}?
[EX A]: 20/273

[EX Q]: Calculate prob of sequence rkk when three letters picked without replacement from {r: 12, k: 3}.
[EX A]: 12/455

[EX Q]: Solve 3*l - 4*y - 18 + 4 = 0, -4*l = 2*y + 18 for l.
[EX A]:
-2