Simple Statistics Question

Dear All,

It has been a long time since I studied statistics. I was wondering if
someone could point me in the right direction regarding which
statistical technique I should be using for the following problem ...

At work we are currently trying to optimise our business practices. We
have measured the time we spend in a number of activities, then changed
practices and re-measured.

I have data which resembles the following:

For 3809 hours of effort spent on a project we spent 5.7% of our time
on Activity A.

After changing our practices, out of 13395 hours of effort we spent
2.5% of our time on Activity A.

What test should I use to determine whether the our change of practice
has had a significant effect (within a certain confidence level).

If someone could just point me in the right direction I will happily
run of to the library to refresh my memory on the subject!

Thanks,
Colin E.

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