The answer is 64 because (2^3) is 8 with an exponent of 2 is 64
There is infinitely many ratios which are equivalent to 5:9. As we know always we can write divide as fraction, so

. We can multiply nominator and denominator by the any number (but the same) and get another numbers but ratio will be the same, so equivalent.
For example
10:18,
15:27
Q10 A20 i think
hope this helps