To determine the amount of juice you will need you will multiply the number of students by how much juice each student will get. This is the idea of grouping. We will need 30 groups of 12 ounces.
30 x 12 = 360 ounces.
You will need 360 ounces of juice.
171.76 ÷ 555 = 0.3094774775
Unit rate in this case would be pages per minute so divide (5/8)pages÷(2/3)minute.
Dividing a fraction can be done as multiplying by the reciprocal.
(5/8)·(3/2)=15/16pages per minute or 0.9375 pages/min.