Courtney's grandmother said . "Your grandpa has different shoe boxes with other stamps His shoebox has just 4 cents 6 cents and cents stamps. Which totals can you make with these stamps? Courtney said , "I wonder why there is a difference between Grandma's and Grandpa's shoeboxes . I like finding the largest total I can't make , but Grandpa's box has an unlimited amount of totals I can't make . I wonder why it works for some and not for others ? " She continues "I am going to investigate which three stamp amounts are like the Grandma's shoebox and which three stamp amounts are like the Grandpa's shoebox . am going to compare three different sets . I will try : 6 cents , 7 cents and 8 cents . Then I will try : 6 cents 9 cents and 12 cents . Finally I will try : 6 cents cents and 9 cents . " Explain how the three different sets are like either Grandma's shoebox or Grandpa's shoebox