Answer:
The entity relationship (ER) data model has existed for over 35 years. It is well suited to data modelling for use with databases because it is fairly abstract and is easy to discuss and explain. ER models are readily translated to relations. ER models, also called an ER schema, are represented by ER diagrams.
Answer:
Disc brake system use a slim rotor and small caliper to halt wheel movement but a drum brake system allow heat to build up inside the drum during heavy braking .
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