It's not rocket science!
Robert: This homework will take me all night!
Simon: Don't be silly mate! It's not rocket science!
It's not rocket science is slang for saying something is not that difficult.
*mate is an informal way of saying friend.
It's not exactly brain surgery.
It's not exactly rocket science.
These are 2 sarcastic ways of saying something is not very difficult.
I got it, thank you.
Swimming isn't rocket science,I should stick to it.
That's right Una!