Identify growth or decay then describe its rate (r=%) y=e^-0.3t

Y=e^-0.3t would better be written as   y=e^(-0.3t), because you want to emphasize that the exponent of "e" is -0.3t.  Enclose the expon. within ( ), ps.

Since the expo is neg, this is expo. decay, and the rate is 0.3 per time period.

For example, if y is = to .5 right now, the next value, after 1 time period, will be 
.5(.3) = .15.