14.6969385 lies between 14 and 15.
I hope it's right! Virtually slap me if it is not.
The correct option will be the last one:
<em><u>Explanation</u></em>
The general equation for sinusoidal function is:
, where
Amplitude,
frequency and
y-intercept
Here the maximum value is 15 and the minimum value is -3. So, the distance between maximum and minimum values is 18. That means, the Amplitude, 
Frequency
is given as 3 and y-intercept
is 6
So, the required function will be:

(16a^6b^8-24ab^9)/4a^6b^8
(4-6ab^1)/a^6b
Hope this helps :)