According to the question,
Man needs to drink = 3 liters of water a day = 3000 ml
Women needs to drink = 2.2 liters of water a day = 2200 ml
Mr. Morrison drank = 880 ml
Mrs. Morrison drank = 700 ml
Total water needed to be drink by both men and women = 3000+2200 = 5200 ml
Total water drank by Mr. and Mrs. Morrison = 880+700 = 1580 ml
Water they both need to drink combined to meet the recommended amounts for the day = 5200 - 1580 = 3620ml
= 3.62 liters
Hope this helps!