Answer:
Robert earned $540
Explanation:
Givens:
- Roberts earns 30% commissions.
- He sold $1800.
To know the amount of money he earned, we just have to find the 30% of 1800. So, we'll express the percentage in a fraction to then multiply it with 1800:

Therefore, Robert earned $540, which represents the 30% commissions of $1800.