Using proportions, it is found that one sandwich costs $4.25.
A proportion is a fraction of a total amount, and the measures are related using a rule of three. Due to this, relations between variables, either direct(when both increase or both decrease) or inverse proportional(when one increases and the other decreases, or vice versa), can be built to find the desired measures in the problem, or equations to find these measures.
Considering x as the cost of a sandwich, the total cost is given as follows:
1.08(3x + 1.75) + 5 = 20.66.
The multiplication by 1.08 is because of the sales tax. We solve for x to find the cost of one sandwich, hence:
1.08(3x + 1.75) = 15.66
3x + 1.75 = 14.5
3x = 12.75
x = 12.75/3
x = 4.25.
Hence one sandwich costs $4.25.
More can be learned about proportions at https://brainly.com/question/24372153
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