Clear[a,α,μ]

((k a[x] t n)/(a[x] n+α[x] c+1))-μ[x]

a[x_]:=1x
α[x_]:=5 x 
μ[x_]:=1(x^2)
Plot[((a[x] n)/(a[x] n+α[x] c+1))-μ[x]-.25/.{n->5,c->0},{x,0,1}]

ContourPlot[((a[x] n)/(a[x] n+α[x] c+1))-1.5 μ[x]-.25/.c->0,{x,0,.5},{n,1,10},Contours->10]

((a[x] n)/(a[x] n+α[x] c+1))-.5 μ[x]

Clear[c]

Manipulate[ContourPlot[((a[x] n)/(a[x] n+α[x] c+1))-1.5 μ[x]-.25,{x,0,.5},{n,1,15},Contours->{0},PlotPoints->30],{c,0,5}]

Manipulate[ContourPlot[((a[x] n)/(a[x] n+α[x] c+1))-1.5 μ[x]-.25,{x,0,.5},{n,1,15},Contours->{0},PlotPoints->30],{c,0,5}]

Plot[((a[x] n)/(a[x] n+α[x] c+1))-μ[x]/.n->7,{x,0,1}]

((a[x] n)/(a[x] n+α[x] c+1))-μ[x]/.n->17

Simplify[D[((a[x] n)/(a[x] n+α[x] c+1))-μ[x],x]]

Solve[((21+136 x+1008 (x^2)-2592 (x^3))/(((1+18 x))^2))==0,x]//N