The first digit is worth 20 (or 1), the second 21 (or 2), the third 22 (or 4), the fourth 23 (or 8), the fifth 24 (or 16), the sixth 25 (or 32) and so on.
This is easily done using the calculator that comes with all Microsoft operating systems which means it is very likely to be available on your computer. To find it, go to help, search for calculator,...
21,125(10) = 0101,0010,1000,0101(2) or if it was a floating point, then the answer is architecture-dependent, on my computer: 20 is 0000000000003440 21 is 0000000000003540 22 is 0000000000003640 21.5...