This problem is just an exercise in entering logarithmic and exponential functions into WeBWorK. Remember that the only logarithm that WeBWorK knows is the natural logarithm, and you write it as log(x). Any other logarithm needs to be expressed in terms of the natural logarithm. You can use a double asterisk or a caret ^ for exponentiation. The number $e$ in WeBWorK is e and the natural exponential can also be written as exp(x).
Try these notations by entering the following functions:

$f(x) = e^x$ .
$f(x) = \ln(x)$ .
$f(x) = 2^x$ .
$f(x) = b^x$ .
$f(x) = \log_2(x)$ .
$f(x) = \log_b(x)$ .