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Carlos rode an average of 9 miles every hour on his bicycle. It is because 3*9=27 and the distance is rate multiplied by time. use the formula and check it!
Hope I helped.
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Looks like your function is

Rewrite it as

Recall that for
, we have

If we replace
with
, we get

By the ratio test, the series converges if

Solving for
gives the interval of convergence,

We can confirm that the interval is open by checking for convergence at the endpoints; we'd find that the resulting series diverge.
Answer:
j-4 is how you show 4 less than a number j