Consider that 620(1.082)x models the average annual health care costs per person, in dollars, as a function of the number of years since 1950.

I guess that you want to calculate the difference between the annual healt care costs in 1950 and today.

The equation is:

C(x) = $620*(1.082)^x

in 1950, we have x = 0 (because is the initial year)

then the cost is:

C(0) = $620*1 = $620.

Now, today, in 2020, we have:

x = 2020 - 1950 = 70

then we have:

C(70) = $620*(1.082)^70 = $154,276.7

So, according to this equation, te difference is:

$154,276.7 -  $620 = $153,656.6