Answer:Justin plans to spend $20 on sports cards. Regular cards cost $3.50 per pack and foil cards cost $4.50 per pack
number of packs of regular cards =r and the number of packs of foll cards = f
Cost of Regular card = 3.50
Cost of 'r' packs of regular card = 3.50r
Cost of Foil card = 4.50
Cost of 'f' packs of Foil card = 4.50f
Justin plans to spend $20 on sports cards so the sum of cost of regular and Foil cards should be less than or equal to 20
The inequality becomes
3.50r + 4.50f <= 20