#### Answer

The total cost is $5544 dollars for 108 pairs of knee guards.

#### Work Step by Step

Each pair of knee guards costs 18 dollars and 308 pairs are purchased. The question asks how much is the total cost of buying this number of pairs of knee guards. Therefore the two numbers are multiplied with each other to find the total cost.
Let $x = $ total cost of buying pairs of knee guards
$18 \times 308 = x$
$5544 = x$
Therefore it costs $5544 dollars to purchase 308 pairs of knee guards.