The total height of the building in the picture has been shown as
x + x + 6
That is, the first two storys have been shown as x feet each and the total height is 26 feet.
That means the two x are actually 20 feet, (if you deduct the 6 feet given)
Total height = x + x + 6
26 = x + x + 6
26 = 2x + 6
Subtract 6 from both sides of the equation
26 - 6 = 2x + 6 - 6
20 = 2x
Divide both sides of the equation by 2 and you now have,
20/2 = 2x/2
10 = x
Therefore, te height of each story is 10 feet!