If a circle's circumference is 15 inches, what is its radius?

If a circle's circumference is 15 inches, what is its radius?

1. $${\frac{{\mathtt{7.5}}}{{\mathtt{n}}}}$$
2. $${\frac{{\mathtt{15}}}{{\mathtt{n}}}}$$  
3. 7.5n
4. 15n