see the attached figure to better understand the problem
we know that
in the triangle ABC
applying the Pythagorean theorem
AC²=AB²+BC²
AC=8 cm
AB=apothem
BC=9.4/2-----> 4.7 cm
AB²=AC²-BC²-----> 8²-4.7²-----> 64-22.09------> AB²=41.91
AB=√41.91-------> 6.47 cm---------> 6.5 cm
apothem=6.5 cm
the answer is
6.5 cm