Question

3,4/5,1 = 1,4/x pleeeeeeeeeeeas

Answer 1

$\frac{3,4}{5,1} = \frac{1,4}{x}$
$\frac{2}{3} = \frac{1,4}{x}$
$2*x=3*1.4$
$x= \frac{3*1.4}{2} =3*0.7=2.1$

Answer 2

3.4/5.1=1.4/x
3.4=3 4/10=3 2/5=17/5
5.1=5 1/10=51/10
1.4=1 4/10=1 2/5=7/5

7/5x=17/5:51/10
7.5x=17/5×10/51
7/5x=2/3
x=2/3:7/5
x=2/3×5/7
x=10/21