To find out how many pet portraits the artist can paint over 14 days, we need to multiply the number of days by the number of portraits painted per day.
The artist paints 3 portraits per day. Therefore, over 14 days, the total number of portraits painted will be:
\[ 3 \text{ portraits/day} \times 14 \text{ days} = 42 \text{ portraits} \]
So, the artist can paint 42 pet portraits during the 14 days at the art fair.