The question goes: The population of bacteria grows at a rate proportional to the number of bacteria at time t. After 3 hours it is observed that 400 bacteria are present. After 10 hours 2000 bacteria are present. What is the initial number of bacteria?

y=ce^kt

y(0)=?

y(3)=400

y(10)=2000

I don't understand how I can solve for the two unknowns: k and c

ex. 400=ce^k(3)