Given a heap represented as an array: $[18,12,17,6,10,8,15,2,5],$

a$.$ Draw the heap:

Provide a visual representation of the given heap by arranging the elements in a complete binary tree.

b$.$ Summarize the two heap properties:

Briefly explain the two essential properties that define a heap.

c$.$ Insert an element into the existing heap and perform heapify:

Insert the element $7$ into the heap and demonstrate the steps to restore the heap properties using heapify.