63 is only 63% of the number 100.
8 is the hundreds, 7 in the tens, and 3 in the ones

Just plug x in and you'll get each y value.
So the answer is A.
The square root is having a sum, ex: 16 and you need to find 2 numbers that are the same numbers and multiply them together and their value equals the said number. Answer: 4 because 4×4=16