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 sum of $500 amounts to 600 in 2 years at simple interest. If the interest rate is increased by 10% it would amount to how much ?

 Option A: $500

 Option B: $700

 Option C: $800

 Option D: $600

 Option E: $300
[EX A]: Option B

[EX Q]: Question: A, B and C invested Rs.6300, Rs.4200 and Rs.10500 respectively, in a partnership business. Find the share of A in profit of Rs.12700 after a year?

 Option A: 3630

 Option B: 9232

 Option C: 8828

 Option D: 2387

 Option E: 3810
[EX A]: Option E

[EX Q]: Question: The ratio between the speeds of two trains is 7: 8. If the second train runs 400 kms in 4 hours, then the speed of the first train is ?

 Option A: 83.5 km/hr

 Option B: 84.5 km/hr

 Option C: 86.5 km/hr

 Option D: 87.5 km/hr

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