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1/5 of a litre is 0.2 litres
1 litre minus 0.2 litres is 0.8 litres so
0.8 divided by 5 (glasses) is 0.16 litres in each glass
B=6 i believe! if you use the pythagorean theorem (a^2+b^2=c^2) then you should be able to turn 8^2 and 10^2 into 64 and 100, respectively. 100-64=36 and the square root of 36 is 6. you can plug it in by calculating 8^2 + 6^2, which equals 100! hope this wasn't too confusing XD
D - the commutative property shoes you cannot flip those numbers without changing the value