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).

Let z = -210 + 300. Let t be (-14)/(-21) - (-398)/6. Let y = -31 + t. What is the greatest common factor of y and z?
18
The given expression is equivalent to -210 + 300 = 90.\nLet t be (-14)/(-21) - (-398)/6 = (14*6)/(21*6) + 398/6 = 884/126.\nLet y = -31 + t = 883/126.\nThe greatest common factor of y and z would be 18 as it divides both of them without a remainder.";.