How can exponential and logarithmic functions be combined?

It really depends on the question and what you want to solve. An exponential function can be written as y = x^2 and if you are solving for y then it will be log (base x) y = 2.

More Examples:

3x = 15

(log both sides with base of 3)

log (3) 3x = log (3) 15

since log (3) 3 = 1 then,

(1) x = log (3) 15

x = log 15 / log 3

= 2.465