The answer is: 10.
Explanation: The numbers are in order by the median/lowest to highest so in that case X wouldn't be 7 because the X would have been next to the 7 not on the other side of the 10.
You would do 20-6 which = 14. + 1 =15. times 8= 120 then divide that by 1/2 = 240 if you do 120 divided by .5 in a calculator thats what you get. i hope that helps you
Answer:
Step-by-step explanation:

multiply by
on each side

add 1 on both sides 
make it equal 0

Factor

answer is 3 and -1