Let S be his total salary. S/3 is for personal use, leaving 2S/3.
Half of this is S/3, spent on household items. He's now used up 2S/3, leaving S/3.
75% of this remaining amount is 75/100=3/4 of S/3=S/4 reserved for emergencies.
In total he has used up S/3 (personal) + S/3 (household) + S/4 (emergencies)
=4S/12+4S/12+3S/12=11S/12, leaving S/12=1000 currency units, so his salary is 12000.
CHECK:
4000 (personal) from 12000 leaves 8000;
Half of 8000 is 4000 (household), leaving 4000;
75% of 4000 is 3000 (emergencies), leaving 1000.