Hello.
5: 5, 10, 15, 20, 25, 30, 35, 40
6: 6, 12, 18, 24, 30, 36, 42, 48
3: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30
Now, find the smallest number they all share.
If you're looking for a faster way, memorize the multiplication/ times table. It definitely helps, especially in advanced math.
Hope that helps!
Disclaimer: Always double check your answers with a reliable source, as mistakes can be made. Never use this, or any, platform to cheat.