Which sinusoid all function gives the height of the rider

First, lets find an expression for the angle on the whell:
Lets say the 'x' is the angle that our passanger have in a given time. We know that in 40 seconds our passanger travels an angle of:
[tex]2\pi[/tex]So, using the rule of three, we can find that in 't' seconds he has an angle of:
[tex]x=\frac{2\pi}{40}\times t\rightarrow x=\frac{\pi}{20}\times t[/tex]now, lets draw again:
So, we can see that the height will be:
[tex]\text{height}=5+(12-12\cos (x))\rightarrow height=17-12\cos (x)[/tex]But we know the expression for the angle x, so:
[tex]\text{height}=17-12\cos (\frac{\pi}{20}\times t)\rightarrow height=-12\cos (\frac{\pi}{20}\times t)\text{ + 17}[/tex]