<u><em>Answer:</em></u>
Mrs. Hong originally had 900 ml of milk
<u><em>Explanation:</em></u>
The complete question is in the attached image
Assume that the amount of milk Mrs. Hong originally had was x ml
<u>We are given that:</u>
1- She used of it to bake the waffles, <u>therefore</u>:
Amount used in baking waffles = ml
2- She used 300 ml to bake a pie
3- Amount left is half the original amount, <u>therefore</u>:
Amount left = ml
<u>We know that:</u>
Total amount = amount used in waffles + amount used in pie + amount left
<u>Substitute with the givens and solve for x:</u>
Total amount = amount used in waffles + amount used in pie + amount left
<u>This means that:</u>
She originally had 900 ml of milk
Hope this helps :)