The task is to generate the correct answer for a given math problem.

[Q]: Problem: if a a b = 2 a - 3 b + ab , then 3 a 2 + 2 a 3 is equal to :
[A]: 7

[Q]: Problem: what is the 149 th digit to the right of the decimal point in the decimal form of 30 / 33 ?
[A]: 9

[Q]: Problem: a train crosses a bridge of length 1500 m in 70 seconds and a lamp post on the bridge in 20 seconds . what is the length of the train in metres ?
[A]:
600 m