Answer:
The cost of a medium pizza is $6
Step-by-step explanation:
This is a system of 3 equations with 3 unknown variables.
The 3 equations are: Small (S), Medium (M) and Large (L)
<em>S + M + L = 18 (1 Equation)</em>
<em>4S + 2M + L = 36 (2Equation)</em>
<em>6S + 5M+ 4L = 86 (3 Equation)</em>
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Clearing the first equation and putting it in the second we have:
<em>4S + 2M + (18 - S - M)</em> = 36 that is <em>3S + M = 18</em>
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Then replacing the clearing of the 1 and 2 equation in equation 3 we have:
<em>6S + 5(18 - 3S) + 4(18 - S - 18 +3S) = 86</em>
that is <em>6S + 90 -15S + 8S = 86</em>
that is 1<em>5S - 14S = 4</em> that is <em>S = 4</em>
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Then replacing S in <em>3S + M = 18</em>; M = 6 (Medium cost $6)