RaTa=360; RbTb=60; Ra=3Rb; TaTb=12

Then evaluate: Ra-Rb+Ta-Tb = ???

Ta=360/Ra

Ta=360/3Rb

Tb=12/Ta

Tb= 12/(360/3Rb)

Ra-Rb+Ta-Tb = 3Rb-Rb+(360/3Rb)-12*3Rb/360

=2Rb+120/Rb -Rb/10

=19Rb/10 +120/Rb