The exact slope is impossible to know for sure, because the function is not written out explicitly. (If we did, we could just do dV/dt evaluated at t = 10.)
However, you can estimate the slope at P by finding the average rate of change between t=5 and t=15, or by taking the average of the slopes of the adjacent secants. There are several ways to approximate the answer, but I don’t think you can find its exact value.
