Final answer:
A clownfish has 84 chromosomes in its muscle cells (somatic).
Step-by-step explanation:
The clownfish has 42 chromosomes in its sperm cells (gametes). Sperm cells and egg cells are both examples of gametes, which are sex cells that are produced for sexual reproduction. Gametes are haploid cells, meaning they have half the number of chromosomes as somatic cells. So, if the clownfish's sperm cells have 42 chromosomes, then its somatic cells, such as muscle cells, would have double that number, which is 84 chromosomes.