'How to substitute a symbol in an expression ? (using sympy)

I try to use 'subs' function to sobstitute the symbol in a numeric value but dosen't work. Anyone can help me? Thankyou!

import sympy as sp
from sympy.solvers import solve
import sympy as sym

x = sp.Symbol('x')

s= (3*x + 0)
r= (2*x + 0.8)
eq=r+s
Xbox=sym.solve(eq)
s.subs(x, Xbox)
print(s)


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