Answer:
[tex]\left \{ {{15Q_a + 20Q_b = 60} \atop {10Q_a + 5Q_b = 30}} \right.[/tex]
Brand A Q 2.4
Brand B Q 1.2
Explanation:
Using Excel solver:
contrains:
c4 = 60
d4 = 30
solve e4 for min
variable cell b2:b3
a        b     c      d     e
        Q Protein Fat Cost
Brand A 2.4 36 Â Â Â Â 24 1.92
Brand B 1.2 24 Â Â Â Â Â 6 0.6
            60     30 2.52
Protein = 60
Fat = 30