One root of the equation $2x^2-8x-m=0$ is $\large\frac{5}{2}$,then the other root and the value of $m$ is _______

Question

$(A) \;m=\large\frac{15}{2}\normalsize ;\text{second root is }\large\frac{3}{2}\\(B)\;m=\large\frac{-15}{2}\normalsize ;\text{second root is }\large\frac{-3}{2}\\(C)\;m=\large\frac{-15}{2}\normalsize ;\text{second root is }\large\frac{3}{2}\\(D)\;m=\large\frac{15}{2}\normalsize ;\text{second root is }\large\frac{-3}{2} $