An oedometer test on a saturated clay soil gave the following results: Cc$=0\mathrm{.}2,$ Cr$=0\mathrm{.}04,$ OCR $=4\mathrm{.}5.$ The existing vertical effective stress in the field is $130$ kPa. A building foundation will increase the vertical stress at the centre of the clay by $150$ kPa. The thickness of the clay layer is $2$ m and its water content is $28\%($a$)$ Calculate the primary consolidation settlement. $($b$)$ What would be the difference in settlement if OCR were $1\mathrm{.}5$ instead of $4\mathrm{.}5.$