Among them, addition and subtraction are called first-order operations; Multiplication and division are called secondary operations.
Formula calculation is a recursive equation calculation, which is an operation to write out the calculation process completely, that is, vertical calculation. When calculating mixed operations, it is usually to work out an expression step by step (step by step, you can't write an equal sign on the original formula), and the process of each step should be written out. Generally speaking, the equal sign should go forward and not be aligned with the first line.