Answer:
Must add 100 milliliters of water
Explanation:
Let
x ----> milliliters of water to add
we know that
Originally
The milliliters of lemon concentrate is equal to the 10% of 100 mL
so

Now
The balance of lemon concentrate is equal to 5%
The milliliters of lemon concentrate is the same
so

solve for x


therefore
Must add 100 milliliters of water