Agatha's weekly allowance is 36.
If she can afford to purchase both four fidgets and three candy bars and nine candy bars and two fidgets, it means that the cost of both options are the same.
4f + 3c = 2f + 9c
Where:
f = cost of one fidget
c = cost of one candy bar
4f + 3(2.40) = 2f + 9(2.40)
4f + 7.2 = 2f + 21.6
4f - 2f = 21.6 - 7.2
2f = 14.4
f = 14.4 / 2
f = $7.20
Weekly allowance = 4f + 3c
4(7.2) + 3(2.4)
28.8 + 7.2 = $36
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