There are 12 girls.
To find this, you must first find how many spectators are adults. Multiply 600 by 80% (0.80) to get 480. Then subtract 480 from 600 to get the number of children (120).
Since it asks to find how many girls there are, we multiply 10% (0.10) to 120. This will give you a final answer of 12 girls.
I hope this helps!