Which is an exponential decay function f (x)=3/4 (7/4)x f (x)=2/3 (4/5)-x. f (x)=3/2 (8/7)-x f (x)=1/3 (9/2)x

The given functions are


Evaluate the functions. 
1. Because 7/4 > 1 and the exponent is positive,
   the function does not decay.
2.Because 4/5 < 1 and the exponent is negative,
    the function does not decay.
3. Because 8/7 > 1 and the exponent is negative,
    the function decays.
4. Because 9/2 > 1 and the exponent is positive,
    the function does not decay.

A composite plot the functions verifies the answer.