A friend has invited you on a skiing trip. It sounds like fun, but it seems expensive and you don't have much money. You say:
I'd love to go, but I don't know if I'd be able to manage it financially.
This is a friendly, polite way to say "no" someone's invitation:
A: Would you care to join us for drinks?
B: I'd love to, but I can't.
I'd love to stay, but I have a lot of work to do.
This is a polite and roundabout way to say "no" (or "maybe not") to something:
I don't know if I'll be able to make it.
I don't know if he's the best candidate for this position.
This means to have enough money for something.
To "manage" to do something means to succeed, even though it's difficult:
Your "finances" are the amount of money that you have. So managing something financially means having enough money (barely) to afford something. English speakers usually use this phrase in the negative form:
We can't manage it financially.
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