8x=784
x=784:8
x=98
--------------
8*98=784
269+x=405
x=405-269
x=136
---------------
269+136=405
540-x=287
x=540-287
x=253
-------------------
540-253=287
x-378=359
x=359+378
x=737
------------------
737-378=359
x:30=90
x=90*30
x=2700
-------------------
2700:30=90
360:x=20
x=360:20
x=18
-----------------
360:18=20