If 1 inch represents 10 miles on a map, then how many inches will represent 900 miles?

A simple way to find this using mathematical methods is to set up a proportion:

Then you would cross multiply getting:

900=10x (then divide by 10 on both sides to get the variable alone)

x=90

So 90 inches will represent 900 miles

the answer to the question is a  

it has the same slope and the same y-intercept.