Answer
$385J/(Kg.K), copper$
Work Step by Step
We can find the required specific heat of the object as follows:
$C_{ob}=\frac{Q_{ob}}{m_{ob}(T-T_{ob})}$
$C_{ob}=\frac{(m_wC_w+m_{Al}C_{Al})(T_w-T)}{m_{ob}(T-T_{ob})}$
We plug in the known values to obtain:
$C_{ob}=\frac{0.103(4186)(22-20)+0.155(900)(20-22)}{0.0380(22-100)}$
$C_{ob}=385J/(Kg.K)$
We can identify the object by its specific heat value -- copper.
