*7. My wife, whose work takes her away from home a lot, has decedied* she needsan* assistant.
10. The town where I was born has completely changed.
*Typos: decided, needs an.
For 9, I’d recommend the answer that, though which is not wrong (at least in BE).
OTOH, for 8, I’d prefer to use which. There is nothing wrong with that there, but it’s just that which sounds better to me.