help me with math

Question

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

4000 cells per hour after the chemical was applied. Strain B started with 6000 cells

and decreased at a constant rate of 3000 cells per hour after the chemical was

applied. When will the strains have the same number of​ cells? Explain.

Answer 1

in 3 hours both are equally at zero bacteria