Imagine that your teacher wanted you to find the midpoint of -3 and 7 on the number line. To do this, you would add up the given values and divide by 2.
(-3+7)/2 = 4/2 = 2
The value 2 is right in the middle of -3 and 7 on the number line. This result is also the x coordinate of the midpoint since the values I used were the x coordinates of the original points.
55x + 10 = 57x....where x = number of months 10 = 57x - 55x 10 = 2x 10/2 = x 5 = x.....they will cost the same at 5 months...they will each cost $ 285 at 5 months