In his physics class, Mario discovered the height, h, in feet of a bouncing basketball after b bounces is given by the formula: h=12 (2/3) b is this growth or decay

This is a geometric sequence which represent exponential decay. For any sequence, if r^2, the common ratio squared, is less than one, it is exponential decay, or:

f=ir^t

If r^2<1, it is exponential decay. In this case r=2/3, so it is exponential decay.