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There is an equal number of motorcycles and cars in the parking lot. They have $$48$$ wheels in total. How many cars are there in the parking lot? 
Overseas Competition->Knowledge Point->Calculation Modules->Basic Concepts of Equation->Linear Equations with one Variable
Let $$x$$ be the number of cars.  $$2x+4x=48$$  $$6x=48$$  $$x=8$$ 