1st day = 425 people
3rd day = 575 people
so in 2 days there is an increase of 575-425 = 150 people.
therefore there is increase of 75 people per day, as attendance is increasing linearly.
So, in 4th day the attendance will be 575+ 75 = 650 people
and in 5th day the attendance will be 575+ 2*75 = 725 people
and in 6th day the attendance will be 575 +3*75 = 800 people
general linear equation will be y = 75x + 425
where y = number of attandancee
and x = number of days