$${\Delta L = \frac{(F/A)L}{E} = \frac{(2,2 \times 10^8\, \mathrm{N/m^2})(0,81\, \mathrm{m})}{2,0 \times 10^{11}\, \mathrm{N/m^2}} \\ = 8,9 \times 10^{-4}\, \mathrm{m} = \underline{\underline{0,89\, \mathrm{mm}}}}$$