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).
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Question: What is 85.89907t in micrograms?

Answer: 85899070000000


Question: Calculate prob of sequence rkk when three letters picked without replacement from {r: 12, k: 3}.

Answer: 12/455


Question: Suppose -b - 3*g = 2*b - 231, -310 = -4*b - 2*g. Suppose -5*k = -10, 5*k + b = 2*u - 0*u. What is the units digit of u?

Answer:
4