Answer:
D. left foot for the accelerator and your right foot for the brake.
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Solution :
Given :
The number of blows is given as :
0 - 6 inch = 4 blows
6 - 12 inch = 6 blows
12 - 18 inch = 6 blows
The vertical effective stress 


Now,

corrected N - value of overburden
effective stress at level of test
0 - 6 inch, 
= 9.86
6 - 12 inch, 
= 14.8
12 - 18 inch, 
= 14.8

= 13.14
= 13