We're the railroads a strength or weakness of the union during the civil war

They were a strength to the Union. They carried soldiers and supplies to the battlefront much quicker, from a few months' march to a week. Having the supplies quicker to the battleground gave the Union the advantage over the Confederates, since the Union could recover much faster from any loss.

4) y=2x+1
5) y=-5
6) y=-1/2x+4