Dear student,
(a) Profit for 1 bag of white cement= Rs8
Profit for 3000 bags of cement= Rs24000
Loss for 1 bag of grey cement= Rs 5
Loss for 5000 bags of grey cement= Rs25000
Total loss= 25000-24000= Rs1000
(b) Loss for 1 bag of grey cement= Rs5
Loss for 6400 bags of cement= Rs28000
Profit for 1 bag of white cement= Rs8
No of bags of white cement needed= 28000/8= 3500 bags
Regards