198+399+157+226=990
286+114+279+21=700
734−(624+8)
=102
-----------
450−84−16
=350
-------------
596-(20+196)=380
900:36=25 5092:38=134, 89712:178=504, 3025:55=55, 93600:300=321
7+х=28 7*х=28 х+21=28 х*4=28
х=28-7 х=28:7 х=28-21 х=28:4
х=21 х=4 х=7 х=7
------------ --------------- --------------- ----------------
7+21=28 7*4=28 7+21=28 7*4=28
18=28 28=28 28=28 28=28