Answer:
a ) See Annex
b) P₁  =  0,0464       or    P₁  =  4,64 %
c) P₄  = 0,92   or   P₄  = 92 %
Step-by-step explanation:
b) P₁ [ X being defective ]  =  P₂   +   P₃
Where P₂  is the probability of X rays machine detects a weld defective and the weld is really defective
And  P₃  is the probability of X rays machine detects a weld defective and the weld is not defective
Then
P₂  =  0,04 *  0,92  =  0,0368
P₃  =  0,96 * 0,01  = 0,0096
Then  P₁  =  0,0368  +  0,0096
P₁  =  0,0464       or    P₁  =  4,64 %
c) P₄ = 0,04 *0,92
P₄  = 0,92   or   P₄  = 92 %