Concept:Average product (AP) is the output produced per unit of labour.It is calculated by dividing total product by the number of workers.Explanation:For the 4th unit of labour, 4 workers produce a total of 60kg.Use the formula:AP=Number of workersTotal productSubstitute the values:AP=460=15kgTherefore, the average product of the 4th unit of labour is 15kg.Answer:C. 15