Answer for the box: -5n+2
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Work Shown:

The common difference is due to us adding -5 to each term to get the next one. Example: -3+(-5) = -8, or -8+(-5) = -13.
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As a way to check if we have the correct nth term formula, plug in values of n to see if we get the correct sequence value
For instance, if n = 1, then

Which matches with the first term given to us.
Or if n = 2, then,

That matches the second term given to us. I'll let you check the others.