If Garlan earned $15 in commission for selling $150 worth of shoes, then his commission rate is 10% (15/150 = 0.1 or 10%). This means that for every dollar worth of shoes he sells, he earns 10 cents in commission.
To find out how much he earned in commission for a different amount of sales, you can multiply the total value of the sales by his commission rate. For example, if he sells $300 worth of shoes, his commission would be:
Commission = Total value of sales x Commission rate
Commission = $300 x 0.1
Commission = $30
So Garlan would earn $30 in commission for selling $300 worth of shoes.