On average, Justin takes 1 less hour to assemble a bicycle than Christina. If working together Justin and Christina can assemble 36 bicycles in a combined 80 hours, how long does it take Justin to assemble a bicycle? Do not include the units in your answer.

Energy cannot be created or destroyed. This statement is known as law of conservation of energy, and it implies that whenever a certain form of energy does change, the loss of this form of energy must have converted into an another type of energy. A typical example is an object falling to the ground: initially, the object has gravitational potential energy. As the object falls down, it loses potential energy (since its altitude from the ground decreases), but it acquires kinetic energy (because its velocity increases). In this example, potential energy has converted into kinetic energy, but the total energy of the object has remained constant.