To buy both the green and the blue bikes would cost $1500. to buy the green and red bikes would cost $750. to buy all three bikes would cost $2000. how much does each bike cost?

Green = g
Blue = b
Red = r

g+b = 1500
g+r = 750
g+b+r = 2000

in the 1st equation solve for b

g+b =1500
b = 1500-g

2nd equation solve for r

g+ r = 750
r = 750-g

now substitute the answers fro. b and r into the final equation.

g+b+r = 2000
g + 1500-g + 750-g = 2000
-g + 2250 = 2000
-g = -250
g = 250

So we k own the green bike is $250.

Blue = 1500- g
blue = 1500-250= $1250

red = 750-g
red = 750-250 = $500

I would go with what she answered bescause I checked over it and it is all correct! :) I know that I didn't do much but sometimes its just nice to get a second opinion! :) 

You're doing something i dont know how to do but search up on google slope calculator maybe that will get you there