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:
