1) 84a + 25a + 7 = 443
109a + 7 = 443
109a = 443 - 7
109a = 436
a = 4

2) 4(9 + 7x) = 21
36 + 28x = 21
28x = 21 - 36
28x = -15
x = -15 / 28

3) 486 / (5x + 2) = 18
486 = 18(5x + 2)
486 = 90x + 36
450 = 90x
x = 450 / 90
x = 5

4) 5(14 + b) + 6b = 258
70 + 5b + 6b = 258
11b = 188
b = 188 / 11
b = 17.09 (rounded to two decimal places)