Sample A $(5$kg$)$ initially at $150$ and sample B $(3$kg$)$ initially at $20$ are placed in a thermally insulated container and allowed to come to thermal equilibrium of $40$ Given the specific heat of sample A is $50011.$

$($a$)$ Determine the specific heat of sample B$.(6$ marks$)$

$($a$)$ Find the entropy change of the whole system.