Answer:
$5.85 = cost for fluffy slime
4r + 2(5.85) = 53.5
Step-by-step explanation:
Let r = cost of regular
   f = cost of fluffy
(1) Â Â 3r + 9f = 84 Â Â Â Â Â Â Â (2) Â Â 4r + 2f = 53.5
4 x (1) Â Â Â 12r + 36f = Â 336
-3 x (2) -12r - 6f = Â -160.5
           30f = 175.5
             f = $5.85 = cost for fluffy slime
4r + 2(5.85) = 53.5
4r + 11.7 = 53.5
4r = 41.8
r = $10.45 = cost for regular