Answer: Evan bought 11 packs of sugar-free gum.
Step-by-step explanation: To find out how many packs of sugar-free gum Evan bought, we can set up an equation based on the information provided: Let X be the number of packs of gum Evan bought. The total cost of the gum, including tax, is $0.89 per pack. Therefore, the total cost of x packs of gum is 0.89x dollars. Evan paid $10.00 and received $0.21 in change. This means the amount he spent is $10.00 - $0.21 = $9.79. Setting up the equation: 0.89x=9.79. To find the value of X we need to divide both sides by 0.89: X=9.79/0.89=11