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Left chicken = x = 20
Double eggs = y = -2
Triple eggs = z = 3
Seven bananas = a = 6
Last equation isn't complete, we can make them all free variables if we want. But since 2 out of the 3 variables are just flipped versions of the original ones, I am gonna interpret that as their additive inverse so:
Right chicken = -20
Flipped eggs = 2
This gives the equation
-20+2d=???
Let the whole equation go to 0. Then solve for d
2d=20
4 bananas = d = 10
