The easiest way to answer this is to put x=0 in the expression and evaluate it: 36+9=45.
Now put x=9 and evaluate it again: 144+9=153, which is bigger than 45 by 153-45=108.
Whenever x is increased by 9 the expression evaluates to 108 more.
To solve this algebraically work out 12(x+12)+9-(12(x+3)+9=12x+144+9-12x-36-9. Note that the constants 9 cancel out, and so do the 12x terms and we are left with 144-36=108. Note that 108 is 12×9. And 9 is the amount by which x was increased, and 12 is the multiplier outside the parentheses.