I'm in 7th grade can somebody just think of 2 goals that I can use that makes sense for math (long term goals)

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 is equivalent to 10/12? options: 10/18 5/6 3/12 9/11

Daniel expanded the expression as shown below -2(-8x-4y+3/4)=-10x-8y-11/4 what errors did he make? check all that apply