Answer:
The number of spells Ginny casts when Luna casts 20 spells is 25
Explanation:
Luna and Ginny each cast magic spells.
The ratio of spells Luna casts to spells Ginny casts = 4:5
Let the ratio be x
So, Luna casts = 4x
Ginny casts = 5x
We are supposed to find what is the number of spells Ginny casts when Luna casts 20 spells
So, 4x=20

Ginny casts =

Hence The number of spells Ginny casts when Luna casts 20 spells is 25