His old apartment cost 1200*12=$<<1200*12=14400>>14,400 per year
His new apartment 1200*1.4=$<<1200*1.4=1680>>1680 per month
That means it cost 1680/3=$<<1680/3=560>>560 per month
So it cost 560*12=$<<560*12=6720>>6720
So he saves 14400-6720=$<<14400-6720=7680>>7680
#### 7680