SOLUTION: 3x + 5y =54 6x + 4y = 72

You should include a question.  The assumption is you want to solve the system for x and y:



2(3x + 5x = 54) --> 6x + 10x = 108

                  -(6x +  4y =  72)

                  ------------------

                          6y =  36  -->    -->  

You want to solve a system of two equations in two unknowns

    3x + 5y = 54      (1)
    6x + 4y = 72      (2)


Divide second equation by 2 (both sides).  Keep equation (1) as is.
You will get

    3x + 5y = 54      (1)
    3x + 2y = 36      (2')


Now subtract equarion (2') from equation (1).
The terms with "x" will cancel each other, since they have equal coefficients.
You will get

         5y - 2y = 54 - 36
            
            3y   =    18

             y   =    18/3 = 6.


To find x, substitute y= 6 into equation (1). You will get  

    3x + 4*6 = 54  --->  3x = 54 - 30 = 24  --->  x = 24/3 = 8.


ANSWER.  x= 8,  y= 6.


CHECK.  To check, substitute the found values into given equations; 
        calculate left sides and compare with right sides.