Answer
See below.
Work Step by Step
a) $P(loose \ keys)=P(loose \ keys|mechanical\ defects)P(mechanical\ defects)=0.27\cdot0.88=0.2376$
b) $P(\text{improperly
connected or poorly welded wires})=P(\text{improperly
connected or poorly welded wires}|electrical\ connects)P(electrical\ connects)=(0.13+0.52)\cdot0.12=0.078$