It's In the System Online book

Investigation 1 - Linear Equations with Two Variables

1.1- Shirts and Caps: Solving Equations with Two Variables

1.2 - Connecting Ax + By = C and y = mx + b

1.3 - Booster Club Memberships: Intersecting Lines

Resources:

Graphing slope intercept form Khan Academy

Practice graphing slope intercept form Khan Academy

Graphing slope intercept/changing into slope intercept practice

Point as a solution to a system game

Investigation 2 - Solving Linear Systems Symbolically

2.1 - Shirts and Caps Again: Solving Systems with y=mx + b

2.2 - Taco Truck Lunch: Solving Systems by Combining Equations I

2.3 - Solving Systems by Combining Equations II

Resources:

Solving systems using elimination game

Identities and no solution equations game