Question

$frac{5,6}{3x+12}=frac{0,4}{3}$

Answer 1

$frac{5,6}{3x+12} = frac{0.4}{3}$ = 3x+12 =
( 3*5.6):0,4=3x+12  
16,8:0,4=3x+12
 42=3x+12
3x=42-12
3x=30
x=30:3
x=10

Answer 2

огромное спосибо