Use x for your variable.
The product of four more than a number and nine is fifteen.

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?

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /

In a newspaper, it was reported that yearly robberies in springfield were up 25% to 265 in 2013 from 2012. how many robberies were there in springfield in 2012?