Answer: 1 ⁸/₂₁ litres
Step-by-step explanation:
First find a common multiple to enable you add them up:
= 21
21 will be the denominator.
Multiply each numerator by the number you get when you divide 21 by the denominator.
= 21/3 = 7
= 7 * 2 = 14
= 21/7 = 3
= 3 * 5
= 15
litres