$4.$ A common polymer used in orthopedic implants is modeled using a single Maxwell element $($see Figure below$).$ When a tensile stress of $1$ MPa is applied for $20$ seconds, the sample reaches a maximum strain of $\backslash (10\backslash \%\backslash ).$ After removal of the stress at $20$ seconds, the strain is $\backslash (2\backslash \%\backslash ).$

a$)$ Draw the strain vs$.$ time curve.

b$)$ Calculate the values for the elastic modulus, E $,$ and the coefficient of viscosity, $\backslash (\backslash$eta $\backslash )$