### Common Core State Standard

### 6.EE.A.2

Write, read, and evaluate expressions in which letters stand for numbers.

*CCSS: 1.OA.D.8, 3.OA.A.4, 3.NF.A.3b, 4.OA.C.5, 5.OA.A.2, 6.EE.A.2*

Choose to practice 1 of 8 skills from addition all the way up to algebra. Whatever skill you choose, you'll need to use that skill to save the people from the monsters, aliens and more!