A kindergarten teacher bought $21 worth of stickers and cardstock for his class. The stickers cost $1.50 a sheet and the cardstock cost $3.50 per pack. The equation 1.5s +3.50 = 21 represents the relationship between sheets of stickers, s, packs of cardstocks, c, and the dollar amount a kindergarten teacher spent on these supplies. Explain how we can tell that this graph represents the given equation: