Graphs of Sine and Cosine · Medium problem

$y=3\cos\!\left(\tfrac{\pi}{3}x\right)+8$

$y=3\cos\!\left(\tfrac{3}{\pi}x\right)+7$

$y=3\cos\!\left(\tfrac{\pi}{3}x\right)+7$

$y=3\cos\!\left(\tfrac{\pi}{3}x\right)-7$