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