answers
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
E E D D F C D E D D  E  F  A  A  F  B  C

18
converges by comparison with $\sum_{n=1}^{\infty}{4\over 2^{n}}$

19
$\sum_{n=0}^{\infty} (n+1)x^{n+3}$ with radius of convergence $R=1$

20
converges by comparison with $\sum_{n=1}^{\infty}{1\over n^{3/2}}$,
which converges by $p$-series test with $p=3/2$.

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makeup answers
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
F E D B F A D E D D  E  F  F  A  E  B  C

18
converges by comparison with $\sum_{n=1}^{\infty}{6\over 3^{n}}$

19
$\sum_{n=0}^{\infty} (n+1)x^{n+4}$ with radius of convergence $R=1$

20
converges by comparison with $\sum_{n=1}^{\infty}{1\over n^{5/2}}$,
which converges by $p$-series test with $p=5/2$.