Find c\displaystyle {c} such that the function
f(x)={x27xc8x23x>c.\displaystyle {f{{\left({x}\right)}}}={\left\lbrace\begin{array}{cc} {x}^{{2}}-{7}&{x}\le{c}\\{8}{x}-{23}&{x}>{c}\end{array}\right.}.
is continuous everywhere.
c=\displaystyle {c}=