Question 1099869
Entire outside volume,  {{{6pi*(2.5/2)^2=6*pi*(5/4)^2}}}, cubic centimeters.
You do not really need all this; you only need to know the 1.25 cm radius.



INSIDE volume for empty space EXCLUDING the wall, {{{6pi*r^2=429}}}


What is the wall's thickness?  Solve for r and then find {{{5/4-r}}}.
Or  {{{1.25-r}}}.