Total Revenue for Producing Eight Units of Output Is $48

Total revenue for producing eight units of output is $48.Total revenue for producing nine units of output is $63.Given this information,the:

A) average revenue for producing nine units is $1.
B) average revenue for producing nine units is $15.
C) marginal revenue for producing the ninth unit is $1.
D) marginal revenue for producing the ninth unit is $15.