Answer: 15
You would do the Reciprocal or Multiplicative Inverse.
You can never divide by a fraction. So instead, you find the recriprocal which is pretty much just flipping the numbers and operations. So instead of dividing, we would multiply. We'd also then flip 1/3 and say its 3/1.
Now your equation is 5 x 3/1 or 5 x 3. Thats 15.