[Precursor]

I have a question that is giving me a bit of trouble and I need some help. So here is the question:



So here is my attempt at a solution:

To find the height of mercury I have used the following equation:

P_gauge = density_air*g*h_air + density_Hg*g*h_Hg

where P_gauge = 3.75 KPa

So I solve for h_Hg and get 2.8 cm. I don't think this is correct. Am I even using the correct method of solving this problem?

[Borek]

Why do you ignore h_sea and h_w?