As per the question, the function you have to write takes two inputs, a number and a function (see function handles) and returns two outputs, the original number and another number. Therefore you must have two variable names before the = in your function declaration and two variable names in the brackets of your function declaration.
Note that g(x) is not a valid variable name.
To get you started, the following declaration would work:
function [a, ga] = mysmallfunction(x, g)
