Exponential functions are in the form [tex]ab^{x} [/tex]. In this equation, [tex]b[/tex] can be determined by figuring out the "common ratio" or the multiplier: the number that you have to multiply each [tex]y[/tex] value to get the next [tex]y[/tex] value. So, what do you have to mulriply [tex]5[/tex] by to get [tex]10[/tex]. Or [tex]10[/tex] by to get [tex]20[/tex]. Your answer to that question is your [tex]b[/tex].
To get your [tex]a[/tex], you simply need to find the [tex]y[/tex] value that corresponds to an [tex]x[/tex] value of [tex]0[/tex]. So, from the chart, what [tex]y[/tex] value corresponds to [tex]x=0[/tex]?
Now, just substitute the [tex]a[/tex] and [tex]b[/tex] you found into [tex]ab^{x} [/tex] and you've got your exponential function.
