(a)
#include "avr/io.h"
int main ( )
{
	DDRB &= ~(1<<0);		
	DDRB = DDRB|(1<<3);	
	OCR0 = 3;			
	TCNT0 = 0;			
	TCCR0 = 0x36;		
	while (1);
	return 0;
}

(b)
#include "avr/io.h"
int main ( )
{
	DDRB &= ~(1<<0);		
	DDRB = DDRB|(1<<3);	
	OCR0 = 3;			
	TCNT0 = 0;		
	TCCR0 = 0x1E;		
	while (1);
	return 0;
}