The actual size of the motor bike = 60 inches.
Bob is planning to create a model that will of 1/5 of the actual size
Size of the model bike = (1/5) * 60 inches
= 1 * 12 inches
= 12 inches
So the size of the model bike that Bob is planning to make will be 12 inches. I hope the procedure is clear enough for you to understand. You can always use this method for solving similar kind of problems in future without requiring any help from outside.