Hello!
To solve this you have to find the ratio between the two cylinders
Cylinder 1 height is 30
Cylinder 2 height is 20
this is a 30:20 ratio
This can be reduced to a 3:2 ratio
Now you look for one that are also equal to 3:2
3 * 7 = 21
2 * 7 = 14
The answers are 3:2 and 21:14
Hope this helps!