Need help ASAP(10 points)

Awater holding tank measures 105 m long, 50 m wide, and 8 m deep. traces of mercury have been found in the tank, with a concen- tration of 60 mg/l. what is the total mass of mercury in the tank? answer in units of kg.

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 : /

Jan accidently ran 7 minutes longer than he was supposed to. write an expression for the total amount of time jan ran if she was supposed to run m minutes