2 (-20)+3 [5/4 (-20)]+5 [2/5 (50]+4 (50)

First off if the beginning of the problem was 2(-20) the answer would be different you would have to use pemdas parenthesis exponents multiply divide add &subtract. You would multiply everything that needs to be multiplied then you would add and subtract what ever needs to be added and/or subtracted then the answer would be 25

The difference is 5,100m?