Explanation:
d = price of 1 drink
s = price of 1 sandwich
3d + 5s = 25.05
4d + 2s = 13.8
we can do this by combining both equations so that they is only one variable left.
e.g. multiply equation 1 by 4 and equation 2 by 3, and then subtract equation 2 from equation 1 :
12d + 20s = 100.2
- 12d + 6s = 41.4
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0 14s = 58.8
s = 58.8/14 = $4.20
3d + 5s = 25.05
3d + 5×4.2 = 25.05
3d + 21 = 25.05
3d = 4.05
d = 4.05/3 = $1.35
so, each drink costs $1.35.