The mean is the sum of all values divided by the total number of values. Then:
[tex]\begin{gathered} Mean=\frac{3+17+10+6+25+17+34+30+13+27+3+0+21+17+13+20+15+20+29+27}{20} \\ \\ Mean=\text{ }\frac{347}{20} \\ \\ Mean=\text{ 17,35} \end{gathered}[/tex]