(3/20 - 1/3) : (9/400 + 1/20 - 1/9) =
(9-20)/60 : (81+180-400)/3600 =
(-11)/60 • 3600/(-139) =
-660/(-139) =
660/139
(5/6 + 3/4) : (625/900 - 685/1000 + 9/16) =
(10+9)/12 : (25/36 - 137/200 + 9/16) =
36=2^2•3^2
200=2^3•5^2
16=2^4
cmmmc=2^4•3^2•5^2=3600
19/12 • 3600/(2500-2466+225) =
19/12 • 3600/259 =
5700/259
