9/10x=1/2x+12

9/10x         =1/2x +12

9/10x -1/2x= 12

(9x-5x)/10 = 12

4x/10        =12

4x             =120

x               =120/4

x               = 30

that is the value of x

9/10x=1/2x+12         1/2  = 5/10   ......so we have

(9/10) x  = (5 / 10)x + 12       subtract (5/10) x from both sides

(4/10) x = 12         4/10 = 2/5

(2/5) x   = 12      to get x by itself, multiply both sides by 5/2

x = 12 (5/2)   = 60 / 2   =  30