Which is the graph of f(x)=3(2/3)^x

Need this asap if anyone can i would be very grateful. if you could show workings that would really

The brain volumes (cm cubed) of 50 brains vary from a low of 904 cm cubed to a high of 1488 cm cubed. use the range rule of thumb to estimate the standard deviation s and compare the result to the exact standard deviation of 175.5 cm cubed, assuming the estimate is accurate if it is within 15 cm cubed

Ineed i been stuck on this question since yesterday