SO easy..... YOu are ICSE student:-
When M.P. is given and no discout is given M.P.=S.P.
So to find rate of sale tax=
Saletax charged= 100+salex%/100*s.p
When M.p is given and sicout to solve the and you will get dicout and you will get sicout and subtitute in formula and you are done!
ALL the BEST