Question

5+7y-12/3=y+13 решить уравнение

Answer 1

$5 + 7y - frac{12}{3} = y + 13$
5 + 7y - 4 = y + 13
7y - 1 = y + 13
7y - y = 13 + 1
6y = 14
$y = frac{14}{6} = frac{7}{3} = 2 frac{1}{3}$

Ну или 
$frac{5 + 7y - 12}{3} = y + 13$
Тогда...
$frac{5+ 7y - 12}{3} - y - 13 = 0$
$frac{5 + 7y - 12 - 3y - 39}{3} = 0$
$frac{4y - 46}{3} = 0$
$y = frac{46}{4} = 11.5$