Can I say "merely" instead of "just"?
Answer from a Native speaker
The "just" here is similar in meaning to "only" or "simply." "Merely" is similar in meaning and is a slightly less commonly used word, but can still be used in this context without changing the meaning of the sentence. It also sometimes has the effect of adding modesty to a statement. Ex: I'm just a university student. = I'm merely a university student. Ex: My computer is not merely a tool for my work, but also a way for me to communicate with others.