Diophantus Updated/Solution

Solution
Inside Amanda.

Proof
Let $M$ be the age in years of Amanda now.

Let $C$ be the age in years of John now.

We have:

So John is $-\dfrac 3 4$ years old, that is, $-9$ months.

That is, John will be born in $9$ months time.

So, right now, John's father is inside Amanda.