Hi, from a quick search , the market prices of 5 room EMs are around $500k-$600k.
You need to have 10% set aside as downpayment for this flat, which is around $50k to $60k.
The next question I have for you is, are you and your wife joint-tenants for your 3-room BTO flat? If yes, that would mean the proceeds of your 3 room Punggol BTO flat would be split evenly between both of you.
Therefore, once you sell the flat, there'll be a surplus of $90k split evenly between you and your wife, which mean you'd have $45k surplus.
On top of that, you'll have to leave a remaining of the amount you took in grant with accrued interest in your CPF account.
The remaining surplus can then be used to finance your new flat.