Translations. Translate and then translate again.
This depicts a composition of translations. It's best to start with just one. So make sure that A''B''C''D'' is off. Type in a translation for A'B'C'D'. Once you get the hang of that, turn A''B''C''D'' on. Type in a second translation. Can you find a single translation that takes ABCD to A''B''C''D''? Click the last box to check if you're right. When you predict three in a row you should move on to another activity.