Answer:
a)<em> Null hypothesis : H₀</em>:  the proportion of defective item of computer has been lowered. That is P < 0.15
<u><em>Alternative hypothesis: H₁:</em></u> The proportion of defective item of computer
has been higher. That is P> 0.15 (Right tailed test)
b)    Test statistic    
c)     Calculate the value of the test statistic = 0.991
d) The critical value at 0.01 level of significance = Z₀.₀₁ = 2.57
e) Null hypothesis accepted at 0.01 level of significance
f) we accepted null hypothesis.
   Hence t<em>he proportion of defective item of computer has been lowered. </em>
Step-by-step explanation:
<u>Step(i)</u>:-
<em>Given the sample size 'n' = 42</em>
Given random sample of 42 computers were tested revealing a total of 4 defective computers. 
The defective computers 'x' = 4
<em>The sample proportion of defective computers </em>
                                                                 
<em>Given The Population proportion 'P' = 0.15</em>
<em>The level of significance ∝=0.01</em>
<u>Step(ii)</u>:-
a)<em> Null hypothesis : H₀</em>:  the proportion of defective item of computer has been lowered. That is P < 0.15
<u><em>Alternative hypothesis: H₁:</em></u> The proportion of defective item of computer
has been higher. That is P> 0.15 (Right tailed test)
b)
     Test statistic    
                        
c)       
                  
                   
       
                       
   Calculate the value of the test statistic Z = - 0.9991
                                    |Z| = |- 0.9991| = 0.991
<u>Step(iii)</u>:-
d) 
         The critical value at 0.01 level of significance = Z₀.₀₁ = 2.57
e)   Calculate the value of the test statistic Z = 0.991 < 2.57  at 0.01 level of significance.
<u><em>Conclusion</em></u>:-
     Hence the null hypothesis is accepted at 0.01 level of significance.
f) 
<em>     The proportion of defective item of computer has been lowered.</em>