`(root(4)(16+h)-2)/h`

function `f(x)=root(4)(x)`

evaluate at a=16

`f(16+h)=root(4)(16+h)`

`f(16)=root(4)(16)=2`

`(f(16+h)-f(16))/h=(root(4)(16+h)-2)/h`

So the answer is `f(x)=root(4)(x)` and `a=16`

`(root(4)(16+h)-2)/h`

function `f(x)=root(4)(x)`

evaluate at a=16

`f(16+h)=root(4)(16+h)`

`f(16)=root(4)(16)=2`

`(f(16+h)-f(16))/h=(root(4)(16+h)-2)/h`

So the answer is `f(x)=root(4)(x)` and `a=16`