What is 0.775 fraction in simplest form?

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?

In a small section of a stadium there are 40 spectators watching a game between the cook islands and fiji. they all support at least one of the two teams. 25 spectators support the cook islands and 16 of these support both teams. how many support only fiji?

What is the value of x? assume that the line is tangent to the circle.