$(40$ Points$)($a$)$ Estimate the activation energy for creep for the alloy having the steadystate creep behavior shown in the figure below. Use data taken at a stress level of $300$ MPa and temperatures of $650C$ and $730C.$ Assume that the stress exponent $n$ is independent of temperature.

$($b$)$ Estimate $lo{n}_s^{}$ at $600C$ and $300$ MPa $.$