To find the equation of the time they spent we need to use the:

Where m is the slope and (x1,y1) is a point of the table.
We can find the slope with:

Using the first two points on the table we have:

Now plugging the values of the slope and the first point into the equation we have that:

Therefore the equation that represents the time they spent is:

where x is the number of people they survey and y is the time it takes.