Complete the circles using the given four basic operators to get the number $20$.

  

$5, 10, 15,$_____, $25$.

$30, 24$, _____, $12, 6$

If BOOK is $43$,

Then PEN is _____

If SCHOOL is $1938151512$,

Then CLASS is _____

If the BAG is $10$,

Then a BOOK is _____

If LION is $50$,

Then TIGER is _____

If HEN is $8514$,

Then a COCK is _____