The rate of change is :
(2010 - 1780)/5 = 230 / 5 = 46
46m per year
Here's the formula for exponential decay:

(where A = new amount, p = principal (starting) amount, k = rate of decay, and t = time)
Let's use what we know and fill in the expression.

And now we solve for t.
Because GH bisects FGI, FGH=HGI
2x+1=3x-9
x=10°
so the measure of HGI is 21°