**Answer:**

7 1/2 or 7.5

**Step-by-step explanation:**

3n=5n-15

We move all terms to the left:

3n-(5n-15)=0

We get rid of parentheses

3n-5n+15=0

We add all the numbers together, and all the variables

-2n+15=0

We move all terms containing n to the left, all other terms to the right

-2n=-15

n=-15/-2

n=7+1/2