Method 1
45/15 = 3
45 is 3 times 15, so the price is 3 times as much.
3 * $300 = $900
Method 2 using unit cost
15 screwdrivers for $300 means
$300/15 = $20/screwdriver
The unit cost is $20 per screwdriver.
For 45 screwdrivers, the cost is
$20/screwdriver * 45 screwdrivers = $900
