To find the amount of oatmeal in ounces for 1 ounce of milk, we use the following proportion

Now, we solve for x.

So, for 1 ounce of milk, the amount of oatmeal is 4/5 ounces.
Now, let's find the amount of milk for 5 1/10 ounces of oatmeal.

Now, we solve for x

Hence, there are needed 6 3/8 ounces of milk to get 5 1/10 ounces of oatmilk.