With the sum of 16 and the difference of 6 what would be the two numbers to solve it

The two numbers are 11 and 5.

Let x be the bigger number
and y be the other number 

x+ y = 16           equation 1
x-y = 6                 equation 2

by addition equ.1 and equ2 

2x = 22 

x= 22/ 2 = 11

by replace it in equation 1

x+ y = 16 

11+ y= 16

y= 16-11=5

Maybe you meant that the circle is incribed in the square, then,

area of square = 144 m^2
=> side^2 = 144 m^2
=> side = sqrt (144 m^2)
=> side = 12 m

since the circle is incribed in the square
diameter of circle = length of a side of square
= 12m

now,
circumference of circle = 2 × pi × r
= 2 × 3.14 × 6 m
= 6.28 × 6 m
= 37.68 m
= 37.7 m