Please can someone help me asap

Agrocery store has 12 lb of trail mix that is 10% banana chips. the store's manager would like to add banana chips to bring the new mix up to 25% banana chips. write and solve a system of equations to find out how many pounds of banana chips manager needs to add.

Me. i can't figure out this question. give an explanation too. .

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.