A group of scientists studied the effect of a chemical on various strains
of bacteria. Strain A started with 12000 cells and decreased at a constant rate of
3000 cells per hour after the chemical was applied. Strain B started with 4000 cells
and decreased at a constant rate of 2000 cells per hour after the chemical was
applied. When will the strains have the same number of cells? Explain.

To determine when the strains will have the same number of cells, first write and solve a system of two linear equations.
The solution to the system of linear equations is
nothing.