Use the information given in the figure below to construct a mathematical model for the number of pounds of salt x, (t), x, (t), and x (t) at time t in tanks A, B, and C, respectively. pure water mixture mixture 3 gal/min 2 gal/min 1 gal/min A B C 100 gal 100 gal 100 gal mixture mixture mixture 5 gal/min 4 gal/min 3 gal/min dx 1 dt dx 2 dt dx 3 dt