Answer:
GH$11,000
Explanation:
For more than 5 sheets, the charge is GH$2000 plus GH$600 for each sheet over 5. That can be described by the formula ...
c(n) = 2000 +600(n -5) = 600n -1000
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For 20 sheets, the charge will be ...
c(20) = 600(20) -1000 = 12000 -1000 = 11000
Barbara will pay GH$11000 for having 20 sheets typed.