You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: Find the equation of a line which passes through A(4, -1) and is parallel to x axis.

 Option A: y=-2

 Option B: y=3

 Option C: y=2

 Option D: y=-1

 Option E: y=0
[A]: Option D


[Q]: Question: If x and y are integers, what is the least positive number of 24x+18y?

 Option A: 3

 Option B: 6

 Option C: 9

 Option D: 12

 Option E: 15
[A]: Option B


[Q]: Question: Two stations A and B are 20 km apart on a straight line. One train starts from A at 7 a.m. and travels towards B at 20 kmph. Another train starts from B at 8 a.m. and travels towards A at a speed of 25 kmph. At what time will they meet?

 Option A: 9

 Option B: 10

 Option C: 11

 Option D: 12

 Option E: 8
[A]:
Option E