Question 380865
Use the t-distribution for small samples. 
The test statistic is {{{t = r*sqrt((n-2)/(1-r^2))}}}.  Then {{{t = r*sqrt(20/(1-(-0.405)^2)) = -1.98}}}. 
Degree of freedom is 22- 2 = 20. 
For 20 df and one-tailed test, critical value is -1.725.  Since -1.725 > -1.98, r is significant at the 5% level.