Find, if it exists, a value c in the interval [1, 4] such that the instantaneous rate of change of f(x) = 12
x.z-dn.net/?f=%5Csqrt%7Bx%7D" id="TexFormula1" title="\sqrt{x}" alt="\sqrt{x}" align="absmiddle" class="latex-formula"> at c is the same as the average rate of change of f over the interval [1, 4]. (If an answer does not exist, enter DNE.)