Fill the 4 litres can up to half and 2 litres can up to half with water then it becomes 3 litres. Half of 4 is 2 and half of 2 is 1 then 2+1=3.
0 measurmnts r nt givn ri8
if you are asked to bring half glass of water would you tell them there are no measurements on the glass so i can't bring
the measurements r not mentioned.this is the main point in the question