power set of empty set = $p(\phi )=\left \{ \Phi \right \} , powerset of singleton set=p(\left \{ \phi \right \})= \left \{ \phi ,\left \{ \phi \right \} \right \}$
as we know if a set contain n element then power set will contain $2^{n}$
so here empty set contain 0 element so p(empty set) contain $2^{0}=1$
and singleton set has 1 element so power set will contain $2^{1}=2$
so for given question |R|=1 and |T|=4 , S= 1*4=4 ans .