Answer: hello  some of your values are wrongly written hence I will resolve your question using the right values
answer:
stiffness = Â 1.09 * 10^-6 N/m
Explanation:
Given data:
Length ( l ) = 16 m
radius of wire ( r ) = 3.5 m
mass ( m ) = 5kg
Distance stretched (  Δl ) = 4 * 10^-3 m ( right value )
average bond length ( between atoms ) = 2.3 * 10^-10 m ( right value)
first step : calculate the area
area ( A ) = πr^2 = π * ( 3.5)^2 = 38.48 m^2
    γ      = MgL / A Δl
          = [ (5 * 9.81 * 16 ) / ( 38.48 * (4.3*10^-3) ) ]
          = 784.8 / 0.165 = 4756.36 N/m^2
hence : stiffness =  γ  * bond length
              =  4756.36 * 2.3 * 10^-10  = 1.09 * 10^-6 N/m