Answer:
Therefore it is save to carry a 62kg adult
Explanation:
From the question we are told that:
Mass 
Height of supporting Rock 
Length of Board
Mass of board 
Mass of adult
Generally the moment of balance about wedge part about is mathematically given by



where

therefore

if N=0 at fallen person

Therefore it is save to carry a 62kg adult
Molarity and molality both describe the concentration of a substance in terms of moles.
Molarity describes the number of moles of a substance per unit of volume, typically per liter (mol/l).
Molality describes the number of moles per unit of mass, typically kilograms (mol/kg).
When determining the molality of a solution, mol/kg can be obtained by finding the number of moles in the substance, and dividing that number by the the total weight in kilograms of that substance.
When determining the molarity of a solution, mol/l can be obtained by dividing the number of moles in a substance by the total volume in liters of that substance.
Answer with Explanation:
We are given that
Force acts on a pebble=
N
Position vector=
m
a.We have to find the resulting torque on the pebble about origin.
Torque=
Substitute the values then we get

Torque=
N-m
By using 
b.

Torque about point (2,0,-3)

N-m