Thermalnuke 0 Junior Poster in Training

Given the following instructions

ADD Rx,Ry,Rz ;Rx <- Ry + Rz
ADDI Rx,Ry,Imm ;Rx <- Ry + Immediate Value
NAND Rx,Ry,Rz ;Rx <- NOT (Ry AND Rz)

Show how you can use the above instructions to achieve the effect of the following:

CLR Rx ;Rx <- 0

I am a newbie to assembly language i personally really don't understand any of this but this is as much as i got and i am most certain that it is wrong, Explanation would be very help full. Im also just here to learn. thank you

ADD Rx,Rx,Rx ; 1's Compliment Rx Rx <- Rx + Rx
ADDI Rx,Rx,1 ; 2's Compliment Rx
ADD Rx,Ry,Rz ; Rx <- Ry + (-Rz)