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

Ex Input:
Problem: if 4 xz + yw = 10 and xw + yz = 20 , what is the value of the expression ( 2 x + y ) ( 2 z + w ) ?

Ex Output:
50 .

Ex Input:
Problem: a train covers a distance of 100 km in 1 hour . if its speed is decreased by 10 km / hr , the time taken by the car to cover the same distance will be ?

Ex Output:
1 hr 6 min

Ex Input:
Problem: a bus trip of 660 miles would have taken 1 hour less if the average speed v for the trip had been greater by 5 miles per hour . what was the average speed v , in miles per hour , for the trip ?

Ex Output:
55