The difference between a and B is 21. What's the difference between a and B

The difference between a and B is 21. What's the difference between a and B

yeyifan1998,
Divide the number of a by the number of B, and the quotient is 4 / 7
A is: 21 (7-4) × 4 = 28
The second is: 21 (7-4) × 7 = 49