You can work out the percentage change and that would help you work out the rate of appreciation :)
The formula is ((new value - old value)/old value) * 100.
So you do 
Therefore the rate of appreciation is 8% p/a.
Ok let’s solve it
5(x-2)^2-20=0
first let’s foil (x-2)
5(x^2-4x+4) -20=0
now distribute the 5
5x^2 -20x +20 -20 = 0
combine like terms
5x^2-20x=0
take the gcf
5x(x-4)=0
x=0, 4
solutions are (4,0) and (2, -20) because the original vertex form a(x-h)^2+k