Write a C++ function to find a node at a given index and sum the values of its parent and child nodes. Start indexing at O Function Arguments head: head of the linked list with at least three values in it index: index of a node; sum this node's parent and child values The node at index will always have at least one node before it and one node after it. Your function should return the sum of the parent and child node. int SumBeforeAndAfter(nod e *head, int index); The linked list structure: struct node int value; node *next; node *prev li Example: Linked list pointed to by head: 4 7 8 22 index = 1 Your function should return 12 For example: Test Result //index = 2