You need to purchase fertilizer to put on your rice farm which is 12 hectares.
Chemical testing of the soil had revealed that each hectare for your particular farm if going to require:

21.9 kg of Nitrogen
21 kg of Phosphorus
11.4 kg of Potassium
2.8 kg of Sulfur

There are two types of fertilizer...
And Type F costs $12 per bag, and contains: 10 kilograms of Nitrogen (N)
8 kg of Phosphorus (P)
7 kilograms of Potassium (K)
1 kg of Sulfur (S).

Fertilizer Type G costs $15 per bag, and has: 11 kg of Nitrogen (N)
13 kg of Phosphorus (P)
4 kg of Potassium (K)
2 kg of Sulfur (S)

I need to find what combination of bags should be bought in order to minimize the total cost, and find out the mimimum cost?

Find the total requirements.

From a quick view, you see that Type G has more P than N, but your land requires slightly more N than P. So, most of your fertilizer would be of Type G. Try buying all G and see what needs to be bought instead of 1, 2 or maybe more bags of F.

Find the total requirements.

From a quick view, you see that Type G has more P than N, but your land requires slightly more N than P. So, most of your fertilizer would be of Type G. Try buying all G and see what needs to be bought instead of 1, 2 or maybe more bags of F.