Question 1071822
<pre><b><font size = 5>
a(x+b)=3x+12

Since that is to be true for all values of x,
it's true when x = 0.  So,

a(0+b)=3(0)+12
  a(b)=0+12
    ab=12

It's also true when a=1, so

a(1+b)=3(1)+12
  a+ab=3+12
  a+ab=15, and since ab=12,
  a+12=15
     a=3

And since ab=12
          3b=12
           b=4

So a(x+b)=3x+12  is really just
   3(x+4)=3x+12

An application of the distributive principle.

Edwin</pre></font></b>