The given answer shows the correct intermediate steps of the data set being sorted with the Quick sort algorithm. The first step is to partition the array around a pivot element, which in this case is 10. After partitioning, the array becomes 10, 20, 15, 18. Then, the same process is applied to the two sub-arrays formed by the partition. The next pivot element is 15, and after partitioning, the array becomes 10, 18, 15, 20. Finally, the last pivot element is 18, and after partitioning, the array becomes 10, 15, 18, 20, which is the sorted array.