I have the following paragraph:
"The contents of a fish tank with 70 fish, of which 10 percent are goldfish, are added to another fish tank with 130 fish, of which 20 percent are goldfish. After the tanks are combined WHAT percentage of the first are goldfish?"
The "what" in question is "WHAT". Should it be kept as "which" to match the previous "which"-'s?
Also, where would one place commas for the sentence?