Perpetual Increasing Annuity

What is the present worth of a perpetual annuity of 10 pounds payable at the end of the first year, 20 pounds at the end of the second, 30 pounds at the end of the third, and so on, increasing 10 pounds each year; interest being taken at 5 per cent. per annum?

H. S. Hall & S. R. Knight, Higher Algebra (1891) · Ch. XVIII. Interest and Annuities, Examples XVIII.b, No. 15