Answer:
(2x+7)/(x+1) = 3; Relation
Lucy bought 4 place-mats
Explanation:
Let the number of place-mats bought by Lucy be equal to x. The total cost of these x place-mats, at $2 each, would be;
2x
Her total cost will then be;
2x + 7; since she bought one doormat at $7.
The total items bought by her is then equal to;
x + 1
Her total average cost can thus be given as;
total cost / total number of items
(2x+7)/(x+1)
Therefore, we can formulate the following relation;
(2x+7)/(x+1) = 3; since the average cost per item was $3
2x+7 = 3(x+1)
2x+7 = 3x + 3
7-3 = 3x-2x
4 = x
Therefore, Lucy bought 4 place-mats