The graph of an exponential function passes through the points (1,6.25) and (3,156.25).
a. (i) Determine the equation of the function in the form f(x)=abx.
b. (ii) Using the equation obtained, compute the value of f(−1).
c. (iii) Comment on how your answer in part (ii) relates to the fact that the x-axis is a horizontal asymptote of any exponential function.