1)6,42+2,31b=15,662)54,6-(y+14)=18,73)6*(3,6x-8,7)=12,64) (a-0,95)*0,18=0,5495)...

1)
$6.42 + 2.31b = 15.66 \\ 2.31b = 15.66 - 6.42 \\ 2.31b = 9.24 \\ b = \frac{9.24}{2.31} = 4$
2)
$54.6 - (y + 14) = 18.7 \\ y + 14 = 54.6 - 18.7 \\ y + 14 = 35.9 \\ y = 35.9 - 14 = 21.9$
3)
$6 \times (3.6 x- 8.7) = 12.6 \\ 3.6x - 8.7 = \frac{12.6}{6} \\ 3.6x - 8.7 = 2.1 \\ 3.6x = 2.1 + 8.7 \\ 3.6x = 10.8 \\ x = 3$
4)
$(a - 0.95) \times 0.18 = 0.549 \\ a - 0.95 = \frac{0.549}{0.18} \\ a - 0.95 = 3.05 \\ a = 3.05 + 0.95 = 4$
5)
$(41.9 - y) \div 4.7 = 3.5 \\ 41.9 - y= 3.5 \times 4.7 \\ 41.9 - y = 16.45 \\ y = 41.9 - 16.45 = 25.45$
6)
$12x - 5x = 3.192 \\ 7x = 3.192 \\ x = \frac{3.192}{7} = 0.456$
7)
$7x + 5x + 0.28 = 9.1 \\ 12x = 9.1 - 0.28 \\ 12x = 8.82 \\ x = \frac{8.82}{12} = 0.735$
8)
$7.7y + 15.4 + 6.5y = 65.1 \\ 14.2y = 65.1 - 15.4 \\ 14.2y = 49.7 \\ y = \frac{49.7}{14.2} = 3.5$