Ellipses below are short delays of a few seconds – to let your machine complete system requests after pressing the letters.
Hold Alt+SysRq and press one by one with small pauses r…e…i…s…u…b/o, b – for reboot, o – for shutdown.
Depending on your keyboard – say, it’s German, and the Right Alt is AltGr actually, then the Alt should be the Left Alt.
If SysRq is missing on your keyboard – try PrintScreen instead. The PrintScreen on multimedia keyboards sometimes is accessible in combination with a Fn button.