.
(a) find the probability that the failure is due to loose keys.
0.88*0.27 = 0.2376 = 23.76%. ANSWER
(b) find the probability that a failure is due to improperly connected or poorly welded wires
0.12*(0.13 + 0.52) = 0.078 = 7.8%. ANSWER
The formulas are self-explanatory . . .