BearLM = {{1, 0, 0, 0, 0}, {0, 1, 0, 0, 0}, {0, 10^7, 1, 0, 0}, {-500,
     0, 0, 1, 0}, {0, 0, 0, 0, 1}};
RollLM[q_] = {{1, 20, Power[20, 2]/(2* 4.2*10^13), Power[20, 3]/(
    6 *4.2*10^13), q Power[20, 4]/(24* 4.2*10^13)}, {0, 1, 20/(
    4.2*10^13), Power[20, 2]/(2* 4.2*10^13),
    q Power[20, 3]/(6 *4.2*10^13)}, {0, 0, 1, 20,
    q Power[20, 2]/2}, {0, 0, 0, 1, q 20}, {0, 0, 0, 0, 1}} ;
Vec11 = {vA, [CurlyPhi]A, 0, 0, 1};
Vec12 = BearLM. Vec11;
VecList1 = {Vec12};
Vec21 = {vS, [CurlyPhi]S, 0, 0, 1};
Vec22 = BearLM.Vec21;
VecList2 = {Vec22};
Gls := {
   {vAR, [CurlyPhi]AR, FQAR, MbAR, 1} ==
    RollLM[qW + 1].Last[VecList1],
   {vSR, [CurlyPhi]SR, FQSR, MbSR, 1} == RollLM[-qW].Last[VecList2],
   vAR - vSR == 8.5*10^(-6) qW*Log[12000/(4.6*10^(-5) qW)]
   };

Res = Solve[
   Gls, {vAR, [CurlyPhi]AR, FQAR, MbAR, vSR, [CurlyPhi]SR, FQSR,
    MbSR, qW}][[1]]

eqs = Flatten[Thread /@ Gls]
vars = {vAR, [CurlyPhi]AR, FQAR, MbAR, vSR, [CurlyPhi]SR, FQSR, MbSR, qW}

partial = Solve[eqs[[1 ;; -2]], vars[[1 ;; -2]]];

last = Simplify[eqs[[-1, 1]] - eqs[[-1, 2]] /. First[partial]]

qwsol = Solve[last == 0, vars[[-1]]]

FullSimplify[last /. First[qwsol]] /. {vA -> 1.1, vS -> 2.2, [CurlyPhi]A -> 3.3, [CurlyPhi]S -> -4.4 }
(* -5.9992*10^-12 *)