ANSWER
Dave's savings at first was $300
EXPLANATION
Let the total savings of Dave and Sam be
Since their savings is in the ratio,
The total ratio
Dave's Savings at first is
and Sam's savings at first is
When each of them donate $40 each, then
Dave's savings is now
or
and Sam's savings is now
Or
The ratio of their savings is now
We can now write the proportion,
This implies that,
This simplifies to,
We cross multiply to get,
We expand to get,
We group like terms to get,
This simplifies to,
We divide through by -2, to get,
Dave's savings at first is,
Therefore Dave's savings at first was $300