What do we do when diving exponents?

The triangles are similar. what is the value of x? x=

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 are the measures of ∠a, ∠b, ∠c and ∠d? explain how to find each of the angle measure.