we have the function
f(t)=3cos(6/5t)
The amplitude of the given function is A=3
The minimum value of the function cosine is for t=-pi
so
(6/5)t=-pi
solve for t
t=-5pi/6
y=3cos((6/5)((5pi/6))
y=3cos(-pi)
y=3(-1)
y=-3
the minimum value is y=-3
therefore
The amplitude is 3 and te minimum is -3