Solve and explain please and thank 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?

What is a possible solutions of the x> 3?

Abus travels 36 miles in 45 minutes. enter the number of miles the bus travels in 60 minutes at this rate.