15=x+13

EASY. subtract 13 from both sides, and it's (x=2)

You clearly did not study the web site that was given to you. You had posts about every 3 minutes for a half hour, at which time you said you didn't understand the web site. I call BS. You had not had time to spend any time looking at it.

x+11=9

Post it and I will check it.

18

x+11=9

You need to move the 11 to the other side. Since it's a positive number, you need to subtract it from both sides;

x = -2

x-17=-9

x=26

No.

Add 17 to both sides.

Remember, you're trying to get the number to the other side. So you add a negative number to both sides. You subtract a positive number from both sides.

Study this site.

https://www.mathsisfun.com/algebra/equations-solving.html

15=x+13

do i do the 15 or 13