Let
x -----> number of years
y ----> number of visitors
we have the ordered pairs
(1, 3,500) and (5, 9,500)
step 1
Find the slope
m=(9,500-3,500)/(5-1)
m=6,000/4
m=1,500 visitors per year
step 2
Find the equation in slope intercept form
y=mx+b
we have
m=1,500
point (1, 3,500)
substitute
3,500=1,500(1)+b
solve for b
b=3,500-1,500
b=2,000
therefore
the equation is
y=1,500x+2,000