Question

What is the value of x in the equation 3x – y = 18, when y = 27?

Answer 1

3x-27=18
   +27  +27
3x=45
/3    /3
x= 15

Answer 2

y = 27

3x-y =18
Lets substitute the equation 
= 3x- 27 = 18
   3x       = 18 + 27
   3x       = 45
     x       = 45/3
     x       = 15

So, lets check if the answer is right

3x- y = 18
3*15 - 27 = 18
   45- 27  = 18
           18= 18   CORRECT !

Therefore, the value of x is 15