Find the missing length.

For question #9 the answer is 24.
The length of EG is basically two times the length of JI (12).
What is 12 times 2? 24!
For question #11, the answer is X = 15
Because 2x+6 must equal 18 doubled we would assume it is 15 because if you insert 15 into the equation we get the answer 36 which is 18 doubled. But! For the full solving of the equation you would do this:
1/2(2x+6) = 18
1x+3= 18
1x+ 3 - 3 = 18 -3
1x = 15
divide
X = 15 !