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).

What is prob of picking 4 y when four letters picked without replacement from yyyyyyyymmmymm?
18/143

Two letters picked without replacement from {u: 2, x: 8}. Give prob of picking 1 x and 1 u.
16/45

Suppose 5*z - 21 = -0*z + 4*c, 0 = -3*z + 2*c + 11. Calculate the greatest common factor of 8 and z.

1