I spent three and a half hours doing my work.(改同义句)

I spent three and a half hours doing my work.(改同义句)
=I spent (three hours and a half) doing my work.

当然，楼上的答案也可以，只是不够标准：
=I spent (three hours and thirty minutes) doing my work.

I spent three hours and thirty minutes doing my work.

I spent three hours and a half doing my work.

I spent two hundred and ten minutes for doing my work.