You should prepare 4 liter of milk because if you prepare 400 mL it wouldn't be enough.
Let's assume
Marcella’s age is x
now, we are given
Justin is 2 years older than one third Marcella’s age
so, Justin's age will be

Let's assume Justin's age is J
so, we get

Aimee is four years younger than 2times Justin’s age
so,
Aimee's age will be

now, we can plug J

now, we are given
Marcella is 63 years old
so, x=63
we can plug x=63 and find A


so,
Aimee's age is 42 years

now, we can plug x=63


so, Justin's age is 23 years
B. because it is spun 45 times. 45 + 45 = 90.
20 goes into ninety 4 1/2 times. it would probably be 18%
(Just an estimate)