Question

How much of a perfume that sells for $35 dollars per ounce should be mixed with a perfume that sells for $15 per ounce to make a 3 oz bottle of perfume that can be sold for $63

Answer 1

Let x =  ounces of $35 perfume
Let y = ounces of $15 perfume.

We want a 3-ounce perfume, therefore
x + y = 3            
or 
y = 3 - x               (1)

We want the 3-ounce perfume to cost $63. Therefore
35x + 15y = 63    (2)

Substitute (1) in (2).
35x + 15(3 - x) = 63
35x + 45 - 15x = 63
20x = 63 - 45 = 18
x = 18/20 = 0.9

From (1), obtain
y = 3 - 0.9 = 2.1

Answer:
0.9 ounces of $35 perfume and 2.1 ounces of $15 perfume.