Ratio of age of Prachi to age of Sakshi 2 : 3 and average age of Sakshi, Prachi and Rupali is 23. When Arjun joins the group average age of these 4 persons is 25 years. Calculate sum of age Arjun and Rupali, if Rupali is 13 years older than Prachi? (a) 40 years (b) 47 years (c) 60 years (d) can't be determined (e) none of these