Is 5 in the solution of x+3>8?
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Answer: D) No; If x is 5, the expression on the left simplifies to 8, making the inequality false.
In other words, if x = 5, then x+3 becomes 5+3 which ultimately becomes 8, but this is not greater than 8 on the right side.
Your steps could look like this
x+3 > 8
5+3 > 8 ... replace x with 5
8 > 8 ... this is a false inequality