Help i will brain list

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?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

If you have 12 feet of string and you cut it into equal length of 5 inches each how much string will be left