Cần gấp chính xác pls

$\dfrac{1978.1979 + 1980.21+1958}{1980.1979 - 1978 . 1979}$

`=` $\dfrac{1978.1979 + 1979 . 21 + 21 + 1958}{1979 . ( 1980 - 1978 )}$

`=` $\dfrac{1979 . ( 1978 + 21 ) + 1979}{1979 . 2}$

`=` $\dfrac{1979 . 1999 + 1979}{1979.2}$

`=` $\dfrac{1979 . ( 1999 + 1 )}{1979 . 2}$

`=` $\dfrac{1979.2000}{1979.2}$

`=  1000`