Thank you for your question!
In order to get the cost of 1 kg of cabbage, divide the cost by the quantity:
1.20/2.5
0.48
Now, multiply the amount for 1 kg to 3.75, because you need 3.75 times the amount.
0.48 * 3.75
1.80
So, it would cost 1.80 pounds for 3.75 kg.
Hope this helped!