text: milk problem? robert sells one gallon cartons of milk (4 quarts) for $3.09 and half gallon for $1.65 each. assume that the number of cents you pay for a carton of milk varies linearly with number of quarts the cartoon holds.    write the partcular equation espressing price in terms of quarts. would it be  q= 1/.72 p p = total cost p = price per quart q = # of quarts c = constant price   3.09 = 4p + c c = 3.09 - 4p  1.65 = 2p + c 1.65 = 2p + (3.09 - 4p) 1.65 - 3.09 = 2p - 4p -1.44 = -2p p = .72  3.09 = 4(.72) + c c = 3.09 - 2.88 c = .21  p = .72q + .21  what you are forgetting is that there can be a base constant price to which the variable price is added.  that constant being c.