9/13 is not a fraction that can be simplified: the two numbers don't have a divisor in common.
Let's bring all the other fractions into their simplest form too:
A.6/10=3/5
B. 2/3 This is the simplest form already
C.36/52 =18/26=9/13 ( I divided both numbers by 2 each time)
.... and we don't have to look further, we have already found the right answer: 9/13 is equivalent to 36/52.
