$13.$ The elevations of the PC$,$ PI and PT of a symmetrical vertical curve are $100\mathrm{.}26$ m $,103\mathrm{.}26$ m and $98\mathrm{.}76$ m $,$ respectively. What is the elevation in meters at the midpoint of the vertical curve?

A$.101\mathrm{.}01$ m

C$.100\mathrm{.}51$ m

B$.101\mathrm{.}39$ m

D$.100\mathrm{.}76$ m