7x + 9 = 100
7x = 100 − 9
7x = 91
$x = \frac{91}{7}$
x = 13

26x − 0,8 = 7
26x = 7 + 0,8
26x = 7,8
$x = \frac{7,8}{26}$
x = 0,3

$\frac{1}{2}x - \frac{1}{3} = \frac{1}{6}$
$\frac{1}{2}x = \frac{1}{6} + \frac{1}{3}$
$\frac{1}{2}x = \frac{1}{6} + \frac{2}{6}$
$\frac{1}{2}x = \frac{3}{6}$
$\frac{1}{2}x = \frac{1}{2}$
$x = \frac{1}{2} : \frac{1}{2}$
$x = \frac{1}{2} * \frac{2}{1}$
x = 1

17,5x − 0,5 = 34,5
17,5x = 34,5 + 0,5
17,5x = 35
$x = \frac{35}{17,5}$
x = 2