The mean weekly sales of a 4-wheeler was 50 units per agency in 20 agencies. After an advertising campaign, the mean weekly sales increased to 55…

The mean weekly sales of a $\displaystyle 4$-wheeler was $\displaystyle 50$ units per agency in $\displaystyle 20$ agencies. After an advertising campaign, the mean weekly sales increased to $\displaystyle 55$ units per agency with standard deviation of $\displaystyle 10$ units. Test whether the advertising campaign was successful. [Given $\displaystyle \sqrt{5}=2.24$, $\displaystyle \mathrm{t}_{19}(0.05)=1.729$]