1)
109a+7=443
109a=443-7
109a=436
a=436:109
a=4
=========
2)
36+28x+21=393
28x+57=393
28x=393-57
28x=336
x=336:28
x=12
------------------
3)
5x+2=486:18
5x+2=27
5x=27-2
5x=25
x=25:5
x=5
=============
4)
70+5b+6b=158
70+11b=158
11b=158-70
11b=88
x=88:11
x=8