Answer:
"void" is the correct answer for the given question.
Explanation:
In the function body the value of balance variable is not return that means we use void return type .The void return type is used when the function does not return any value .
If the function are int return type that means it return "integer value ".
if the function are double return type that means it return the "double value" .
The complete implementation of this method is
public void deposit(double amount) // function definition
{
balance = balance + amount; // statement
}