2.58% is the change from 815 to 836
Calculation steps:
[( 836 - 815 ) ÷ 815] x 100 = 2.58%
Formula
Percentage change = [(836 - 815) / 815] x 100
Subtract the new number by the original number
836 - 815 = 21
21 ÷ 815 = 0.025766871165644172
0.025766871165644172 x 100 = 2.58%