(A number) plus eight must be greater than 13. Hmm well we know that 5 plus 8 is 13. So any value larger than 5 added to 8 will give us more than 13, yes?
If you look at the set that you're given, the values which will make the inequality true are 5.5, 6 and 6.5.
5.5 + 8 = 13.5 (This is greater than 13) 6 + 8 = 14 (Still greater than 13) 6.5 + 8 = 14.5 (Yay)
The solution requires than you solve for x. x has 8 being ADDED to it. We can undo this by SUBTRACTING 8 from each side.
x > 13 - 8 x > 5
This is the solution.
For the last part, notice that the inequality is STRICT. It is NOT a "greater than or equal to".
"or equal to" would mean we could include the value 5 in our solution set. But since the inequality is strict, it excludes the value 5.