  The following class of retarded integro-differential equations in a Banach
space
  \[
  \dot{x}\left(t\right)=Ax\left(t\right)+\int_{0}^{t}b\left(t-\tau\right)Lx_{\tau}d\tau+Kx_{t};\,\,t\geq0,
  \]
  are taken into consideration in this study. The delay term $Lx_{\tau}$ of
this equation is inserted into the integral as a convolution product with a
scalar kernel. We prove the well-posedness of the problem under investigation
using the Miyadera-Voigt perturbation and the theory of semigroups. We also
explore the spectral analysis of an associated abstract Cauchy problem.
