Pressure & Hydrostatic Pressure

[sunes123]

Hello, I would like somebody to help me with few simple questions for my homework. I did try to solve them but I failed at few of them. Here are the two papers I need to help with. I need help with the highlighted excerises. I tried some basic formulas for pressure and hyrdostatic pressure but as I said I failed a lot. May you guys please explain how can I achieve the result on these exercises. On the page with exercises 11) 12) and 13) Could you please explain i depth the 12 and 13? If you can't read the exercise just skip it. I would like to thank you in advance.

Homework Statement

2. Homework Equations
Well I tried to work with
P = H ⋅ ρ ⋅ g
also I tried for the stone 13)
V = (m ⋅ S) : ρ (of the stone)

The Attempt at a Solution

I would like to apologise for not posting my attempts as it is just mess on my paper. I tried using these formulas but did not help. I was only given these. Cant really figure out much.

 

[haruspex]

Please post an attempt by typing it in. Use LaTeX if you can, or just use the superscript, subscript and special character (Σ) buttons above.