Fill in the blanks
 
(i) \((​30​ + ​50​) + ​90​ =\) ​​ \(+\) ​90​ \(=\) ​
 
(ii) \((​-30​ + ​50​) + ​40​ =\) ​​ \(+\) ​40​ \(=\) ​