If
( 5 4 )m ( 2 1 )n

then
mlog 5 4 nlog2

and we shall find
m n log2 log5/4 .

Using Euclid's algorithm the result can be represented as a continued fraction.
log2 log5/4 =3+ Q log5/4

where 0< Q log5/4 <1. So
log2 log5/4 =3+ 1 log5/4 Q =3+ 1 9.4087788 =3+ 1 9+ 1 2.4463109

giving the first approximation 28 9 . Repeating the algorithm:
log2 log5/4 =3+ 1 9+ 1 2+ 1 2+ 1 4+...

Truncating this continued fraction gives the successive approximations 59 19 , 146 47 and 643 207 .