Answer:
16 balls.
Explanation:
Let x represent the golf balls Ricardo begin with.
Ricardo lost 6 golf balls while playing yesterday. So the number of remaining balls would be
.
He bought a box of 12 golf balls, then lost 4 on the course today.
We can represent this information as:

We have been given that now Ricardo has 18 golf balls. So we will get:

Solve for x:



Therefore, Ricardo has 16 balls to begin with.