Question 130490
Nope, not (b).  You could test that answer by plugging in any of the x values and seeing if you get the right y.  I use 0 because I like when life is easy.  (b) is y=81(1/3)^x/6.  So if x=0, y=81(1/3)^0/6 = 81(1)=81.  But the table says that when x=0, y=27.  So that didn't work.  The answer is (d).  You got the rate (1/3) and the exponent (x/6) right.  You just got tricked by the fact that the table starts at x=-6 instead of at x=0.