The underlined portion of the sentence "una la computadora" is incorrect because it combines two articles in a way that does not conform to the rules of Spanish grammar. In Spanish, you should only use one definite or indefinite article before a noun.
In this case, "una" is an indefinite article meaning "a" in English, and "la" is a definite article meaning "the." You should choose one based on whether you want to refer to the computer in a general sense (using "una") or specify it as a particular computer (using "la").
So, the correct forms would be either "una computadora" (a computer) or "la computadora" (the computer), but not both together.