I need help finishing this problem. I need to write an exponential function of the form $\displaystyle y=ab^x$whose graph passes through the given points. The points are (1,4) and (2, 8/3), the 8/3 is a fraction. I find a in the last set of points, and then use that to substitute for a in the top set, but after that I can't figure out how to simplify and find b. I know it has something to do with logs.(Doh)

Any help is appreciated.