Question

An equation is shown 5x+3x= 5x + 15/2. What value of 3x makes the equation true?

Answer 1

x= 2.5 or 5/2
5x + 3x -5x = 15/2
=> 3x= 15/2

Answer 2

Note:  3x = 15/2   ;  

Divide EACH side of the equation by "3" ; 
______________________________________
3x / 3 = (15/2) / 3 ; 

x = (15/2) / (3/1) =  15/2 * 1/3 =  (15*1)/(2*3) = 15/6 = (15/3)/(6/3) = 5/2 
 = 2.5.
______________________________________________________
So, the equation is true when x = 2.5 ;  and when 3x  = 7.5 ;
                                                              and when 8x = 20.
_______________________________________________________