8. The specimen of copper wirer drawn from a large lot have the pollowing breaking strongth (in kg weight] 578,572, 570, 568,572,578,570, 572,598, 544 , Test whether the mean breaking strength of the lot may be taken to be 578 kg weight at 5% level of significance

This is a conjunction.  you can solve them separately then join them.

2(3-x) + 5 ≤ 39  

6 - 2x + 5 ≤ 39  

11 - 2x ≤ 39

-11          -11

     -2x  ≤ 28

      /-2      /-2

      x   ≥ -14  notice the ≤ switch directions because I divided by a negative

or

     -14 ≤ x

2(x - 3) + 5 ≤ 39

2x -6  + 5 ≤ 39

2x  -1 ≤ 39

2x  ≤ 40

/2       /2  

x ≤ 20

and join them

-14 ≤ x ≤ 20