How much do you spend on these extras each month?

你每个月在这些额外的东西上花多少钱？

How much did you spend on buying a school uniform?

你买校服花费了多少钱？

The time you spend on an ad hoc project tends to be fairly short.

你花在一个特别项目上的时间往往是相当短的。

Next, you should decide how much time you should spend on different subjects.

接下来，你应该决定一下在不同科目上花多少时间。