Question

10(100-x)+2x=3(x+9)-28

Answer 1

$10(100-x)+2x=3(x+9)-28\to \\\\ 1000-10x+2x=3x+27-28\to \\\\ -10x+2x-3x=27-28-1000\to \\\\ -11x=-1001(-1)\to \\\\ 11x=1001\to \\\\x= \frac{1001}{11} \to \\\\x=91$

Answer 2

10(100-x)+2x=3(x+9)-28
1000-10x+2x=3x+27-28
-10x+2x-3x=27-28-1000
-10x-x=27-1028
-11x=-1001.(-1)
11x=1001
x=1001/11
x=91