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.

[EX Q]: Question: A car during its journey travels 30 minutes at a speed of 60 kmph, another 45 minutes at a speed of 80 kmph, and 1 hours at a speed of 70 kmph.The average speed of the car is

 Option A: 63.07 kmph

 Option B: 64 kmph

 Option C: 75 kmph

 Option D: 80 kmph

 Option E: None of these
[EX A]: Option D

[EX Q]: Question: If the ratio of a to b is 2 to 3 and the ratio of b to c is 1 to 5, what is the ratio of a to c?

 Option A: 4/15

 Option B: 1/3

 Option C: 2/15

 Option D: 4/5

 Option E: 7/6
[EX A]: Option C

[EX Q]: Question: x and y are integers. x + y < 11 and x > 6. What is the smallest possible value of x - y ?

 Option A: 1

 Option B: 2

 Option C: 4

 Option D: -2

 Option E: -4
[EX A]:
Option C