Use mercury barometer to fing height of building

[stuplato]

A mercury barometer reads 700.0 mm on the roof of a building and 715 mm on the ground. Assuming a constant value of 1.29 kg/m3 for the density of air, determine the height of the building.
.
My setup was finding the difference in the pressures for mercury and get 15 mm Hg
Then use Hg density = 136000 to get a pressure using P=pgh
So P will equal 1999200
then subtract atmosphere pressure and divide the result by 12.642 (pg)
But the answer is wrong... Where did I go astray?

 

[Fermat]

I haven't checked anything else, but the specific gravity of mercury is 13.6, so its density is 13.6 times greater than water, so density of mercury is 13.6*10^3 = 13,600 kg/m^3.
You have 10 times that value, 136,000, or that a typo ??