If
400 mL
Capacity of 5 glasses = 2 Litres
When we convert a larger unit (L) to a smaller unit (mL) we multiply.
1 Litre = 1000 mL
Hence 2 Litres = 2 × 1000 = 2000 mL
Capacity of 1 glass = Total capacity ÷ No. of glasses
Capacity of 1 glass = 2000 ÷ 5
= 400 mL