Fluid mechanics

Density of oil = 0.85 x 1000 kg /m^3 = 850 kg /m^3
Dynamic viscosity of oil = 850 x (3.53 x 10^-4) Pa-s = 0.3001 Pa-s

Area of one slant side of prism = (0.2/cos(45)) x 2 m ^2 = 0.5657 m ^2
Hence, viscous force acting on one slant side of prism
= 0.3001 x 0.5657 x (0.15/h)

Total viscous force acting on the two sides of prism
= 2 x 0.3001 x 0.5657 x (0.15/h)
Hence, 10 = 2 x 0.3001 x 0.5657 x (0.15/h)
i.e. h = 2 x 0.3001 x 0.5657 x 0.15/ 10 m = 0.00509 m = 5.09 mm