So far, she used 750mL of the lemonade, that means there is 250 mL left of lemonade. I found the answer by multiplying 150 x 5 = 750 and then, I know that there is 1000 mL in one litre so, I subtracted 750 mL to 1000mL which equalled 250. If you don't understand my explanation please message me.