Ok, I hope im right. (Others correct me if im not. But when I worked out this problem I got y is approximatly 4,882 attendees after 6 years.
Gathering info from the graph I created a table
(0,20) , (1,30) , (2,45), ...
I found the difference between the points listed. For example, 30÷20 is 1.5. So, each point is multiplied times 1.5 to continue the sequence.
Use the equation: y=a(1+r)^t
Remember what each variable stands for. That way you can plug in the correct information
Continuing..
y=a(1+r)^t
y=20(1+1.5)^t ; combine like terms
y=20(2.5)^t
b) Plug in the # of years. 6 in our case, everywhere you see a t
y=20(2.5)^6
y is approximately equal to 4882.8125
Round because we can only have whole numbers. we're talking about people.
I hope I got this right. But, if not, I tried