This is the 10474th most frequent Russian word.
взаимно
Mutually.
In this sentence, 'взаимной' (mutual) describes a shared, balanced, or reciprocal sentiment between two individuals.
Мы познакомились, и наша симпатия оказалась взаимной.
We met, and our sympathy turned out to be mutual.
Here, 'взаимно' (mutually) is used as an exclamation to reciprocate the gratitude expressed by the first speaker.
Ты благодаришь меня, а я скажу: взаимно!
You thank me, and I say: mutually!
In this case, 'взаимный' (mutual) specifies that both sides share an equal interest in art.