Write a system of equations and solve.

Let R, C, B represent prices of Red Bull, chips, and Bagel Bites, respectively.
.. 2R +1C +2B = 9
.. 3R +2C +3B = 14
.. 5R +3C +3B = 20

These equations have solution
.. R = 2.50
.. C = 1.00
.. B = 1.50

A can of Red Bull costs $2.50.
A bag of chips costs $1.00.
A box of Bagel Bites costs $1.50.

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If you want to solve these by hand, you can add the first two equations and subtract the third to find the value of B. Then you can double the first equation and subtract the second to find the value of R. Then you can use the first equation to find the value of C.