All related by 10's every move to the right is 10x larger than the one to its left
Since deciliter is two steps away from milliliter it is 10 x 10 or 100 times as large.
If the question is meant to be a trick then the answer is 99x larger.
It should read "A deciliter is how many milliliters" ofr "a milliliter is how much of a deciliter?" Once you say larger than you could be confusing subtraction with multiplication. How much larger than 30 is 3? Answer is clearly 27. How many times as large as 3 is 30? Answer is clearly 20. How many times larger than 3 is 30? Hmmmm? Which one of the two does he mean? I am sure your teacher meant you to consider multiplication, but just in case, I included the "trick" answer.