How to solve a problem using substitution method

there are different types of substitution but the solved question is simultaneous equation using substitution method I only solved one example I hope it helps. It's in the picture above .If you need more examples just chat me up on the comments and I will be glad to solve more for you and also if this is not the substitution you expected ,chat me using the comments slot .

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