MATLab does not solve for my variable and only solves the root of the equation

Hello, I'm new to MATlab, here is the code and the equation:

syms a H Q x y z b c d e f g h
eqn = x + y*a + z*H + b*a^2 + c*H^2 + d*a^3 + e*H^3 + f*a*H + g*a^2*H + h*a*H^2 == Q;
solutions = solve(eqn, a)

solutions = 

variables x y z b c d e f g and h are all constants but they are long numbers so I decided to write them like this. I would like MATlab to solve for a but it just gives me the root of the equation which is useless to me. I even tried replacing the other variables like Q and H with constant to no avail. Even with the only variable being a MATlab still solves for roots instead for a...

[Torsten]

What else apart from the roots of the third-order polynomial in "a" do you expect as solution of your problem ?

To get a numerical solution, you have to substitute your long numbers into the solution using MATLAB's "subs". Maybe this is what you mean.

[Primoz]

I want an equation that looks something like this: a = b*h + c*h^2...

Because I need to make an excel table where the on the top I have Q and on the left side H and inside the table the a values.

[Torsten]

You get three solutions for "a" because you want to solve a polynomial equation of degree 3 in "a":

https://en.wikipedia.org/wiki/Cubic_equation

If you write your equation as

eqn = b1 + b2*a + b3*a^2 + b4*a^3 == 0

with

b1 = x + z*H + c*H^2 + e*H^3 - Q

b2 = y + f*H + h*H^2

b3 = b + g*H

b4 = d

you get the three "a" values as follows (a bit more compact than in @Walter Roberson 's answer):

syms b1 b2 b3 b4 real
syms a 
eqn = b1 + b2*a + b3*a^2 + b4*a^3 == 0;
asol = solve(eqn,a,'MaxDegree',3)

asol = 

Answer 1

[Walter Roberson]

syms a H Q x y z b c d e f g h
eqn = x + y*a + z*H + b*a^2 + c*H^2 + d*a^3 + e*H^3 + f*a*H + g*a^2*H + h*a*H^2 == Q;
solutions = solve(eqn, a, 'maxdegree', 3)

solutions =