Solving Complex Equations Using MATLAB

I am having trouble solving complex equations using the solve command. There are 3 variables I am solving for and I have 2 equations to solve for them but matlab is not able to simplify the equations down to solve for the missing variables. I am also trying to get a graph to display these relations when it is complete. I am trying to solve for L and D in terms of n.

clear;
syms D n L
%density
p=1000;
%Specific Heat
Cp=4182;
k=0.598;
Pr=7.01;
%dynamic visc
m=1.002e-3;
%pressure drop
dP=5000;
%mass flow rate
m_dot=23.9234;
%Cmin
C_min=32258.1;
%UA
UA=125634;
%Reynold's Number
Re=38399.4*(1/(n*D));
%Friction Factor
f=(0.79*log(Re)-1.64)^-2;
%Pressure Drop Relation
%eqn1 = 5000==f*((16*m_dot^2*L)/(p*pi^2*D^4))*(1/(2*D))

h = Cp*((4*m_dot)/(n*pi*D^2))*(1/2)*f*Pr^(-2/3)
eqn1 = UA==h*n*pi*D*L
L = solve(eqn1,L)
simplify(L)
disp(L)
eqn2 = 5000==f*((16*m_dot^2*L)/(p*pi^2*D^4))*(1/(2*D))

%this only displays a number equal to D, I want it in terms of n but n is
%not in the equation
D = solve(eqn2,D,"Real",true)

Answer 1

[Walter Roberson]

Q = @(v) sym(v);
Pi = Q(pi);

syms D n L
%density
p = Q(1000);
%Specific Heat
Cp = Q(4182);
k = Q(598)/Q(10)^3;
Pr = Q(701) / Q(10)^2;
%dynamic visc
m = Q(1002)/Q(10)^6;
%pressure drop
dP = Q(5000);
%mass flow rate
m_dot = Q(239234)/Q(10)^4;
%Cmin
C_min = Q(322581)/Q(10)^1;
%UA
UA = Q(125634);
%Reynold's Number
Re = Q(383994)/Q(10)^1*(1/(n*D));
%Friction Factor
f = simplify((Q(79)/Q(10)^2*log(Re)-Q(164)/Q(10)^2)^-2)

f = 

%Pressure Drop Relation
%eqn1 = 5000==f*((16*m_dot^2*L)/(p*pi^2*D^4))*(1/(2*D))

h = simplify(Cp*((Q(4)*m_dot)/(n*Pi*D^2))*(Q(1)/Q(2))*f*Pr^(Q(-2)/Q(3)))

h = 

Notice that if you take the denominator of f, the term involving log(n), and multiply the two parts by 100, that the expression becomes the same as the 79*log(191997/(5*D*n)) - 164 that shows up in h. So later in the calculations those two log terms cancel, leaving only a fraction.