Question

{[904-4 ×(8-×)]:8-21} :9=10

Answer 1

{[904-4 ×(8-×)]:8-21} :9=10
[904-4 ×(8-×)]:8-21=10×9
[904-4 ×(8-×)]:8-21=90
[904-4 ×(8-×)]:8=90+21
[904-4 ×(8-×)]:8=111
904-4 ×(8-×)=111×8
904-4 ×(8-×)=888
4 ×(8-×)=904-888
4 ×(8-×)=16
8-x=16:4
8-x=4
x=8-4
x=4