Question

How many will you eat (change the voice)

Answer 1

The voice of the given sentence can be changed as shown and explained below:

How many will be eaten by you?

or

How many mangoes will be eaten by you?

Explanation

An interrogative active remains interrogative in passive too.

Active How many + will + S +  V1 ?

Passive How many + O + will + be + V3 + by + S?

Answer 2

Answer:

How many mangoes will be taken by you.