#### Answer

The mean number of flu vaccinations in a day is $144.7$.

#### Work Step by Step

Solve for the mean by adding the nine numbers together then dividing the result by $9$:
Number of flu vaccinations in a day
$=\dfrac{122+135+146+159+128+147+168+139+158}{9}=\dfrac{1302}{9}\approx 144.7$