A chunk of silver has a heat capacity of 42.8 J/°C and a mass of 181 g. How do you calculate the specific heat of silver?

is defined as ##J//(K*kg) or J*K^-1*kg^-1##
(=energy per degree per kilogram of mass)
So you just divide heat capacity of the object by the mass:
##c_”silver”=(42.8J//K)/(0.181kg)~~236J/(K*kg)##
Extra :
Officially, specific heat is defined as the amount of energy needed to raise the temperature of ##1kg## by ##1K##. Since a temperature difference of ##1K## is equal to one of ##1^oC## this is no problem.
Since the SI-unit of mass is ##kg## in stead of ##g## the official answer should be: ##236J//(K*kg)## or ##236J*K^-1*kg^-1##
But most people use the earlier notation of ##J//g*^oC##
which will turn out to be ##0.236J//g*^oC##