You can solve this in a long way so that you will understand
the relationship of the increase in the number of memberships sold.
First week = 5 memberships
Second week = 8 memberships (5 + 3)
Third week = 11 memberships (8 + 3)
Fourth week = 14 memberships (11 + 3)
Fifth week = 17 memberships (14 + 3)
Total after 5 weeks = 55 memberships sold (5 + 8 + 11 + 14 +
17)