ADDITIONAL PROBLEM FOR EXTRA CREDIT: Two solid steel shafts $(G=77\mathrm{.}2$GPa are connected to a coupling disk $B$ and to fixed supports at A and $C.$ The diameter of shaft $AB$ is $40mm$ and that of shaft $BC$ is $38mm.$ For the loading shown, determine $(a)$ the reaction at each support, $(b)$ the maximum shearing stress in shaft $AB,(c)$ the maximum shearing stress in shaft $BC.$