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).

How many millilitres are there in 7/2 of a litre?
3500

Solve 4*s = -t + 10, 7*t + 3*s + 1 = 2*t for t.
-2

Suppose 5*r - 4 - 7 = -3*k, -4*r + 3*k + 25 = 0. Suppose -r = 3*f - 7*f. What is the units digit of f?

1