Answer:
The formula would be
T(n) = 64 (-3/4)^n, n=0,1,2,...
or sometimes
T(n) = T(n-1)(-3/4), T(0) =64, n=0,1,2,...
Explanation:
The common ratio is -3/4, i.e.
(-3/4) * 64 = -48
(-3/4) * 48 = 36
(-3/4) * 36 = -27
...
The formula would be
T(n) = 64 (-3/4)^n, n=0,1,2,...
or sometimes
T(n) = T(n-1)(-3/4), T(0) =64, n=0,1,2,...
Note: Would have been easier if the choices were supplied.