I need help with geometry

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?

Which of the following is the maximum value of the equation y=-x^2+2x+5 a. 5 b. 6 c. 2. d. 1

Hi i’m not sure how to do question 20 if u could explain how to do it that’d b great