Question 172955
10.    2=12*x+7*(1-x)

10.    2 = 12*x + 7 - 7*x 
10.    2 = 12x -7x +7
10.    2 = 5x +7
10.    2 - 7 = 5x +7 - 7
10.    -5 = 5x + 0
10.    -5 = 5x
10.    -5 * 1/5 = 5x * 1/5
10.    -1 = x *5 * 1/5
10.    -1 = x * 1
10.    -1 = x   or x = -1

Be sure to substitute 1 back into the original equation to confirm that the solution is -1.