Answer
$P$(exactly one subsystem in System B fails) = $30.72$%
Work Step by Step
$P$(system B working) = $0.9639$ (as per question c)
Here,
$P$(system B working) = $P$(both subsystems working) + $P$(any 1 subsystem working).
$0.9639$ = 0.6561 + $P$(any 1 subsystem working).
$P$(any 1 subsystem working) = $0.3078$.
$P$(any 1 subsystem working) = $30.78$%.
