You can put this solution on YOUR website!
So. 40/5x2 = 8x2=16, else your teacher would have written 40/(5x2)
Therefore your final result is 16-4=12
explanation: always do operations in parentheses first, starting by the innermost in case you have nestling pairs of parentheses. However, do not put parentheses where there aren't any.
You solved this exercise wrongly because you solved it as if it were written:
40/(5(3-1)) - 4. that is you put in a non-existing parenthesis.
Ciao from Italy