Greetings , I was solving a list of practice exercises when I got to this question, and I quite can't understand what to do about it. Could you please help me?

this is the question

Being a a real number and the imagnary part of the complex number zero, so a is:

(2+i)/(a+2i)

a)-4

b)-4

c)1

d)2

e)4

I appreciate the time you took.

Thank you.