The next received 2/3 of the remainder. That means the youngest received 1/3 of the remainder. That one third was $6. If 1/3 = $6, then 2/3= $12 the total money the two younger received $18
The oldest received 7/13 the other two then received 6/13 so 6/13 = $18 18/6 = 3 1/13 = $3 3 * 13 = $39