The absolute value of the amplitude is the coefficient of sin or cos, so either f(x)=2cos(aaaax)+aaaa or f(x)=−2cos(aaaax)+aaaa. Since it is the reflection of its parent function g(x) = cos(x) over x-axis, we determine that it must be f(x)=−2cos(aaaax)+aaaa
Vertical shift is the constant term, but you need to consider the direction of the shift. Shifting downwards means a negative constant term, so f(x)=−2cos(aaaax)−11.
We also know that the period of h(x)=acos(bx+c)+d is 2πb. You can solve the equation 2πb=6π7 to get the remaining blank.