Decay modelling problem using Simulink

Hello everyone,

I have a question regarding a modelling problem. The problem statement is :

In a certain year we had a sample of radioactive P buried. After 10 years the sample was dug up and 90% of P was present , 8% of Q was present and 2% of R was present. So basically decays is as follows P decays to Q decays to R . If we run this for 1000 years , when will we get the largest amount for Q? I need help on how to start with this problem on Simulink so that a search function is used to find the k value that achieves the largest amount of Q.

The decay equations are :

dP/dt = -k1*P

dQ/dt = -k2*Q + k1*P

dR/dt = k2*Q

Thank you for your help in advance.