For the function y= -1+6cos(2pi/7(x-5)) what is the maximum value?

The maximum value is actually the maximum of y

So, you don't need to care about the stuff inside cosine function,

Cosine function is always within the range of [-1,1]

So here, ymax = -1 + 6* 1 = 5

The answer would be (c)

I’m pretty sure the answer is a