What brick is this?

[iOerlie]

I've been building all the old sets from my childhood. But I lost 1 instruction book. So I tried to search it on the internet by searching a brick and then look for all the sets it appeared in. But I can't find it. Maybe you can help me out. It looks like this brick: https://brickset.com/parts/6015235/brick-4x4-18° But without the cutouts (the slopes are solid).

 

please help me! Thanks in advance!

[NathanR]

Bricklink is a fantastic resource when it comes to mould variations.  That brick has part ID 50373, but the older variant (without the stud notches) is part 2399:

https://www.bricklink.com/v2/catalog/catalogitem.page?P=2399#T=C

There's a fair few old sets which featured it.  If you're missing an instruction book, then you can often download them for free from Lego customer service, or somewhere like lego.brickinstructions.com

Which set are you trying to build?

 

[iOerlie]

Thanks!

It's the victory cup racers set (6539).

Again. Thanks for your help!