Andrea brought a total of 21 fish for her aquariumShe bought 9 fewer angelfish than guppiesHow many and guppies did she buy?

Let the number of guppies be \(x\). Then the number of angelfish is \(x - 9\).

$$x + (x - 9) = 21$$

$$2x - 9 = 21$$

$$2x = 30$$

$$x = 15$$

So, Andrea bought 15 guppies and \(15 - 9 = 6\) angelfish.