How am i supposed to do this without a calculator?

Bismuth-210 is an isotope that radioactively decays by about 13% each day, meaning 13% of the remaining bismuth-210 transforms into another atom (polonium-210 in this case) each day. if you begin with 233 mg of bismuth-210, how much remains after 8 days?

Iwill make brain if you me correctly fill this out needs due today pls and send it back to me (click the link and you will get it)

What is the range? can’t seem to find it out