What do i solve first in this equation

Can someone 50 first drop menu 0.80 or 0.75 or 1.20 or 4.00 second drop menu 4.00 or 0.75 or 0.25 or 3.75 3rd 15,6,10, or 9 4th yes or no

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?

Sole with work in 10 years, the average number of hours of tv watched per week by teenagers dropped from 23.9 to 21.4. find the percent of change.