An vector of  int named a that contains exactly five elements has already been declared and initialized. In addition, an  int variable  j has also been declared and initialized to a value somewhere between 0 and 3. 
Write a single statement that assigns a new value to the element of the vector indexed by  j . This new value should be equal to twice the value stored in the next element of the vector (i.e. the element after the element indexed by  j ). Do not modify any other elements of the vector!