Which graph best shows the function f(x) = 4(3)−x to represent the rate at which a radioactive substance decays?

B

Step-by-step explanation:

The exponential function has the form where a is the starting value or y-intercept. B is the rate of change and x is the variable typically time. In this situation, has starting value 4, rate 3 and a -x.

Normally an exponential curve glides left to right growing steeper as it goes. But a -x flips this behavior. The curve starts very steep then gradually slows down. This means only graphs B or D are options. Since only graph B of these two has a y-intercept at 4, graph B is the solution.