Converting the standard system of measurement to the metric system?
Linear equations are the leadin to geometry  but you have to understand how to solve it before you can move on to harder geometry concepts  which plays into figuring out square footage of houses, how much paint you'll need to paint all the walls in a room, how many tiles you need to tile a kitchen... just cook up some home improvement projects! I'd love to say "we need to refloor the kitchen because our kid is studying linear equations."
