Nsolve rantz not possible to plot
ClearAll["Global`*"];
cinv1 = 40;
cinv2 = 4;
cinv3 = 3;
h2 = 1.4;
h3 = 1.2;
alpha = 0.04;
z = 20;
p = 0.06;
cop1 = 0;
cop2 = 1;
cop3 = 1.5;
l2 = 0.1;
l3 = 0.17;
teta2 = 0.19;
teta3 = 0.1;
co2 = -0.1;

smax = 40;
c = 1;

Plot[Solve[{s12 == ((cinv1 -
         cinv2) + ((cinv2 - cinv3)*((s12 teta2)/(
          Sqrt[ (teta2 - teta3)] Sqrt[
           c s12^2 teta2 - (2 alpha z)/c]))))/((1/(teta2 -
           teta3))*((teta2*cop3 - teta3*cop2) + (teta2*h3*l3*E^(p*t) -
            teta3*h2*l2*E^(p*t)))), s12 > 0}, s12, Reals], {t, 0, 10}]

"*Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result*"
"*Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result*"
"*Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result*"
*"General::stop: "Further output of !(*
StyleBox[
RowBox[{"Solve", "::", "ratnz"}], "MessageName"]) will be suppressed during this calculation""*

s2 = Solve[{s12 - ((cinv1 - cinv2) + ((cinv2 - cinv3) ((s12 teta2)/
          (Sqrt[(teta2 - teta3)] Sqrt[c s12^2 teta2 - (2 alpha z)/c]))))/
           ((1/(teta2 - teta3))*((teta2*cop3 - teta3*cop2) +
           (teta2*h3*l3*E^(p*t) - teta3*h2*l2*E^(p*t))))} == 0, s12];
Plot[s12 /. s2 , {t, 0, 59}]

f1a = s12 /. a;

f1 = Transpose[{b, f1a}];

ceiling1 = ListLinePlot[{f1},
PlotRange -> {{0, 20}, {0, 40}},PlotStyle -> {Black, Dotted, Thickness[0.003]}];

curve1 = Interpolation[f1];
intersec2a = FindRoot[curve1[x2] - t12[x2, l2], {x2, 0}];
intersec2 = x2 /. intersec2a;