65. A
concentrated load of 
is applied to a
rectangular-cross-section beam as shown in the figure. The beam is
simply-supported and has a rectangular cross section with width and height of 
and
,
respectively. If the allowable bending stress is 
and the maximum probability of
failure is designed to be 
, determine the maximum length of
the beam. Assume that 
and 
are independent.
Answer:
