As we know y is inversely proportional to x2,⇒y=x2k​,k is some constant.......(i)Also when x=4 then y=2Using equation (i)⇒2=16k​⇒k=32.......(ii)Now, when x=21​then, ⇒y=4kPutting value of k from (ii)⇒y=4×32=128