Concept:Form linear equations from the given conditions and solve them to find the value of P.Explanation:Let the ages of P, Q, and R be P, Q, and R respectively.From the first condition:P+2Q+R=59⋯(1)From the second condition:3P+Q+R=68⋯(2)From the third condition:P+3Q+3R=108⋯(3)Multiply equation (2) by 3:9P+3Q+3R=204Subtract equation (3) from this equation:(9P−P)+(3Q−3Q)+(3R−3R)=204−1088P=96P=12Thus, the age of P is 12 years.Answer:D. 12 year