Question 1:

public class Multiplies
{
 public static void multiplyOf15()
 {
   for(int i=0; i<100; i++)
      if(i%15==0)
        System.out.println(i);
 }

 public static void main(String [] args)
 {
    multiplyOf15();     
 }
}

Q1- 

public class Multiplies
{
 public static void multiplyOf15()
 {
   for(int i=0; i<100; i+=15)
     System.out.println(i);
 }

 public static void main(String [] args)
 {
    multiplyOf15();     
 }
}

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Question 2:

error: int x=1;  x is not defined before assigning a value
error: infinite while loop

output:
X is 0
X is 1
X is 2

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Question 3: 
See assignment.pdf

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Question 4:

public class Factorial
{
  public static int getFactorial(int n)
  {
   int fact = 1;
   for (int i=1; i<=n; i++)
      fact *= i;
   return fact;
  }
  public static int getFactorial(int n)
  {
   int fact = 1;
   int i=1;
   while(i<=n)
   {
      fact *= i;
      i++;
   }
   return fact;
  }
  public static int getFactorial(int n)
  {
   int fact = 1;
   int i=1;
   do
   {
      fact *= i;
      i++;
   } while(i<=n);
   return fact;
  }


  public static void main(String [] args)