CFAI GB example doubt

on page 75, reading 33,solution to 2 ii. it says " to stay ahead of inflation without eroding the principal value of his portfolio.stern needs to earn 13.8 % this will increase to 14.3% after $50000 donation"

how is the 13.8 and 14.3% arrived at. Is it 10.8% +3% inflation? but why 10.8%. ?

130/1200 = 10.8