All lines that are parallel to JC

Can someone check my answer? you : )

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?

Define multiplicative inverse. give an example of a number and its multiplicative inverse.