Give the step-by-step reasoning process and then the final answer. Cleo and Ignacio placed 30 of their marbles in a jar on a Monday. They took 3/5 of the marbles from the jar the next day and divided them equally. On the third day, Cleo took 1/2 of the marbles remaining in the jars. How many marbles did Cleo have on the third day?
On the first day, Cleo and Ignacio took 3 / 5 * 30 marbles = 18 marbles from the jar. When they shared the marbles, each got 18 marbles / 2 people = 9 marbles / person. The total number of marbles remaining in the jar is 30 marbles - 18 marbles = 12 marbles. On the third day, Cleo took 1 / 2 * 12 marbles = 6 marbles from the jar. The total number of marbles she has on the third day is 6 marbles + 9 marbles = 15 marbles.
The final answer: 15.