An inspection using NDT reveals that a very large, steel plate of yield stress 200 MPa and Poisson's ratio (1/3) has a crack at the centre of length 21 mm which is orientated along the x-axis. If the plate is subjected to far field tensile loading of magnitude 196 MPa and is assumed to be in a state of plane strain, determine the extent of the plastic region at the crack tip, along the x-axis. Express your answer in mm to 1 decimal place.