Answer:
1 plain = $0.75; 1 cheese = $0.95; 1 super = $1.25
Step-by-step explanation:
We have three conditions
(1) 5P = 3S
(2) Â S = C + 0.30
(3)  P = C – 0.20              Substitute (3) into (1)
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(4)  5(C – 0.20) = 3S          Substitute (2) into (4)
   5(C – 0.20) = 3(C + 0.30)   Remove parentheses
     5C – 1.00 = 3C + 0.90    Add 1.00 to each side
          5C = 3C + 1.90     Subtract 3C from each side
          2C = 1.90         Divide each side by 2
           C = $0.95        Substitute C into Equation (2)
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           S = 0.95 + 0.30
           S = $1.25        Substitute C into Equation (3)
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           P = 0.95 – 0.20
          P = $0.75
1 plain = $0.75; 1 cheese = $0.95; 1 super = $1.25