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]: 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]: Calculate prob of sequence ggrr when four letters picked without replacement from {r: 2, b: 6, t: 6, g: 4}.
[A]: 1/3060


[Q]: Solve 9*d = 4*d - t - 7, 7 = d + 3*t for d.
[A]:
-2