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

[EX Q]: Problem: if 4 xz + yw = 10 and xw + yz = 20 , what is the value of the expression ( 2 x + y ) ( 2 z + w ) ?
[EX A]: 50 .

[EX Q]: Problem: a number x is mistakenly divided by 10 instead of being multiplied by 10 . what is the percentage error in the result ?
[EX A]: - 99 %

[EX Q]: Problem: in what time will a railway train 40 m long moving at the rate of 36 kmph pass a telegraph post on its way ?
[EX A]:
4 sec