These two rectangles are similar which is a correct proportion for corresponding sides

to make the proportion we make the ratio of the similar sides

For example

4/8 = 12/x

or we can write it as 4/12 = 8/x

or 12/x = 4/8

So last option is correct

10cm

step-by-step explanation:

ik

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional