If common sense, rather than a principle of physics, tells you that two quantities are equal, then select "Find equivalent quantity."

For instance, suppose the problem is, "A train leaves for Boston from New York at the same time a car leaves for New York from Boston.  The train travels at a constant speed of 2 m/s for 5 hours.  The car makes the same trip in 4 hours.  How fast was the car travelling?" To solve this, you first seek the speed of the car via the principle 'average speed = distance/time.'  Next you must find the distance traveled by the car.  You know the distance traveled by the car is the same as the distance travelled by the train.  Thus, you can select "Find equivalent quantity" to justify adopting the subgoal of finding the train's distance given your goal of finding the car's distance.