Kathi starts with number. she adds 3 to her number then doubles the resut. finally, she sustracts 7. if she ended with 9, what number did she start with?

If the number is x, then 2*(x+3)-7=9 due to that you subtract the result of double of x+3. Adding 7 to both sides, we get 2*(x+3)=16. Next, we divide both sides by 2 to get x+3=8 and subtract 3 from both sides for our final result, x=5