Subtract RAM[1] from RAM[0] and put the result in RAM[2]. Or, put another way: RAM[2] = RAM[0] - RAM[1].
RAM[1]
RAM[0]
RAM[2]
RAM[2] = RAM[0] - RAM[1]
RAM[0] = 6 RAM[1] = 12
RAM[0] = 6
RAM[1] = 12
RAM[2] = -6