Marcus loves being a big brother.
He is a whole year older than his sister, so he thinks he has a lot to teach her.
Helping his sister is his favorite thing ever.
The problem is, Sienna doesn't always want to be helped.
She's a smart kid and she likes to work things out by herself.
But a new challenge is about to make Sienna feel a bit nervous . . .
like maybe she might just need a teeny-weeny bit of help.
You see, tomorrow is...