1)
11/13 = x/10,4
=>
x = 10,4*11/13
=>
x = 8,8
2)
2/7 = x/12,6
=>
x = 12,6*(2/7)
=>
x = 3,6
3)
x/4,5 = 3/7,5
=>
x = (3/7,5) * 4,5
=>
x = 1,8
4)
x/2,4 = 8/1,6
=>
x = (8/1,6)*2,4
=>
x = 12
5)
4,5/x = 5,4/1,8
=>
x = 4,5/(5,4/1,8)
=>
x = 1,5
6)
5,1/8,5 = 2,4/x
=>
x = 2,4/(5,1/8,5)
=>
x = 4