Roger gets $ 4 0 $40dollar sign, 40 per day as wages and $ 4 . 5 0 $4.50dollar sign, 4, point, 50 as commission for every pair of shoes he sells in a day. His daily earnings goal is $ 1 1 2 $112dollar sign, 112.

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 For this case we have the following variable:
 p = number of pairs of shoes
 The equation that represents the problem is:
 f (p) = 4.50p + 40
 To achieve your daily goal we have:
 4.50p + 40 = 112
 We clear the value of p =
 4.50p = 112-40
 p = 72 / 4.50
 p = 16 (pair of shoes)
 Answer:
 an equation to determine how many pairs of shoes, p, Roger must sell in a day to meet his daily earnings goal is:
 f (p) = 4.50p + 40
 the number of pairs of shoes he must sell to meet his daily earnings goal is: 
 p = 16 (pair of shoes)