If the acreage decreases by the factor x (where 0<x<1) per year then in 1925 its acreage is 9x, in 1926 its acreage is 9x2, and so on. 2002-1924=78 years, so 9x78=1.
78log(x)+log(9)=0, 78log(x)=-log(9), log(x)=-log(9)/78=-0.01223 approx, x=0.9722=97.22%.
So the glacier decreases in acreage by 100-97.22=2.78% per year.