arduino leonardo pwm frequency change

hie ,
i want to generate pwm pulses of duty cycle 30% and 50% of frequency 50khz at pins 5 and 3 ,am using it in ac to dc converter for mosfet switching… am new to this am using arduino leonardo board
i have written this code , how do i get 50khz of frequency.

void setup() {
analogWrite(3,128)
analogWrite(5,77)

}

void loop() {
analogWrite(3,128)
analogWrite(5,77)

}
plz do guide me