Draw a picture!! This almost always helps. Assign variables to all changing values. List everything you know: Which variable do you know about? Which variable are you trying to figure out? Label your picture with variables and constants (to avoid confusion, do not assign names to constant values). Figure out how the variables are related, and write down an equation. This is where you bring in knowledge from outside of calculus, typically geometry or physics. If the variables represent two sides of a right triangle, use the Pythagorean theorem. If the variables represent the radius and volume of a sphere, use the formula for volume in terms of radius. You don't have to express one of the variables in terms of the other -- just find an equation that involves both. If there are more than two variables, find a relationship to eliminate one. Differentiate your equation(s) with respect to time. Solve for the rate of change of the variable you want in terms of the rate of change of the variable you already understand. If a variable assumes a specific value under some conditions (for example the velocity changes, but it equals 2 mph at 4 PM), replace it at this time. Remember to plug-in after differentiating. (Why?) Convert that information into an answer to your question.