solving

B=2pi(R+T/2)(A/360)      Divide both sides by 2 pi

B/2pi =  (R+T/2)(A/360)     Now mutiply both sides by   360/A

360AB/2pi = R+ T/2            Now subtract R from both sides

360AB/ 2pi    - R    =   T/2      now multiply both sides by 2    <=======I'll let you finish !