Complete Question
The complete question is shown on the first uploaded image
Answer:
a
The torque produced by the pile of rocks is
b
The distance of the single for equilibrium to occur is
Explanation:
From the question we are told that
The mass of the left rock is 
The mass of the rock on the right 
The distance from fulcrum to the center of the pile of rocks is 
Generally the torque produced by the pile of rock is mathematically represented as

Substituting values
Generally we can mathematically evaluated the distance of the the single rock that would put the system in equilibrium as follows
The torque due to the single rock is

At equilibrium the both torque are equal

Making
the subject of the formula

Substituting values
Atoms<span> are made of three types of sub-atomic particle: neutrons and protons in the nucleus and electrons orbiting the nucleus. </span>Some<span> materials are </span>radioactive<span> because the nucleus of each </span>atom<span> is unstable and gives out nuclear radiation in the form of alpha particles, beta particles or gamma rays.</span>
I believe the blank would simply be behaviour adaptations. Behavioural adaptations are behaviours that organisms demonstrate to help them better survive and reproduce in a habitat. Hope that helps!!