Concept:The mean equals the sum of all values divided by the number of values. Rearrange to find the missing cost.Explanation:Total cost of five books =5×3.25=16.25.Cost of four books =11.75.Cost of the fifth book = Total cost − Cost of four books.=16.25−11.75=4.50.Answer:The fifth book cost GH₵ 4.50, which is option D.