I get:
(20b^10)/(10b^20) =
((1.024 x 10^13)(b^10))/((10 x 10^19)(b^20)) =
(1.02400 x 10-7)*(b^-10)
But I don’t have a calculator and just using the desktop.
Works out when replacing “b” with 5 in both the original equation and the solution. Checked with “b” = 3 as well.