Answer:
The statement for the question is following:-
a[j]=a[j+1]*2;
Step-by-step explanation:
We have to modify the element at the index j.Since the value of j is between 0 to 3 and the vector contains exactly 5 elements.So j will not exceed the size of vector a.
Now what we have to assign the value at index j is the value double at index next to j that is j+1.So the statement will be
a[j]=a[j+1]*2;