A student saves the train ticket number that he has obtained when traveling by train. The train ticket numbers are stored on the table in the order (10, 6, 18, 3, 12, 4, 13, 27). The tickets will be sorted from the smallest to the largest ticket number to find out the order of the smallest to the largest seats they have ever occupied.

Based on this case, provide an explanation and illustration on how to sort test numbers using the Merge-sort algorithm!