Bonjour,
1) à la surface, P = P(atmo) = 1013 hPa = 101300 Pa
2) A 10 m de profondeur :
P = P(atmo) + ρgh
Soit : P = 101300 + 1030x9,8x10 = 101300 + 100940 = 202240 Pa
3) P = 4,0.10⁵ Pa
⇔ P(atmo) + ρgh = 4,0.10⁵
⇔ ρgh = 4,0.10⁵ - 1,013.10⁵ = 298700 Pa
⇒ h = 298700/ρg = = 298700/(1030 x 9,8) ≈ 29,6 m