Code show no plot although there is no error message?

Questions
1

SubPlus[k]/SubMinus[k] == 4/5;
A[t_] := (c0/(1 + (SubMinus[k]/SubPlus[k])) )(
Exp [-t (SubMinus[k] + SubPlus[k])] + (SubMinus[k]/SubPlus[k]))
B[t_] := (c0/(1 + (SubMinus[k]/SubPlus[k])) )(
1 - Exp [-t (SubMinus[k] + SubPlus[k])])
Plot[{A[t]/c0, B[t]/c0}, {t, 0, 10}, PlotStyle → {Blue, Red},
PlotLegends → “Expressions”,
AxesLabel → {“time”, “Concentration”}]

2

Because you did not assign values to the expressions.

kp = 4;
km = 5; 

A[t_] := (c0/(1 + (km/kp)))*(Exp[-t (km + kp)] + (km/kp)) 

B[t_] := (c0/(1 + (km/kp)))*(1 - Exp[-t (km + kp)]) 


Plot[{ A[t]/c0, B[t]/c0}, {t, 0, 10}, PlotStyle -> {Blue, Red}, 
AxesLabel -> {"time", "Concentration"}, PlotRange -> All]