¿dónde está la computadora?

a. encima de la mesa.

b. debajo de la papelera.

c. encima de la puerta.

d. aquí en el reloj.

A.
It is easier to understand if you look for "clues".
Comput should tell you it's computer and when you think of mesa, you think of mess and usually at a table there is some type of scraps left over from some activity!

Where is the computer?
On the table.

What are the main think you have to do in this question i speak spanish i can .

The answer to this question is 18