If it’s falling at a constant rate during the period, then we can conclude that it fell (3.4 mb/hr)(5 hr) = 17 mb.
Now we just need to convert mb to mm Hg, using the given scale.
![image](https://i0.wp.com/78.media.tumblr.com/5e5de16697744dd49a3c0f13ebc79605/tumblr_inline_pdsj4ccMvN1qio24w_540.png?w=852&ssl=1)
Solve that for x and you get roughly 12.8.
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