Mixing it up

I start with two full mugs, one containing milk and the other containing tea, in exactly equal amounts. I transfer 3 spoonsful of milk from the first mug to the second, and stir thoroughly. Then I transfer 3 spoonsful from the now-milky tea in the second mug back into the first mug.

Which is greater: the amount of tea now in the first mug or the amount of milk now in the second mug?

If you are stumped by last issue's puzzle, here is the solution.

For some challenging mathematical puzzles, see the NRICH puzzles from this month or last month.