we know that
the total lemonade is 1 1/2 liter
She pours 1/4 of a liter of lemonade into a thermos
Her brother drinks 2/5 of the remaining lemonade
the remaining lemonade is equal to
1 1/2-1/4=3/2-1/4=5/4 liters
Multiply by 2/5
(5/4)(2/5)=10/20=1/2 liter
therefore
answer is option
C. (1 1/2 - 1/4) x 2/5