I assume you're talking about the instantaneous rate of reaction in chemistry.
- draw the tangent (touches it at one point only) to the curve at the point which you have been asked to find it at
-find the slope (rise over run) of this tangent
-firstly identify the acid and the base on the left side of the reaction
-the acid and its CONJUGATE BASE will differ by one proton (conjugate base will have 1 less proton)
-the base and its CONJUGATE ACID will also differ by one proton (conjugate acid will have 1 more proton)