Answer:
168 cm.
Step-by-step explanation:
If each book has an equal distance of 12 cm and total books are (20-6) = 14
then, total distance is (12*14) = 168.
I hope this is correct. Feel free to correct me if I'm wrong.
The first one because the left bound is included [ and the right one is not )
0.3*42 this gives you a 30% discount
3/10*42 this gives you a 30% discount
0.03*42 this gives you a 3% discount
3 *4.2 This is not a discount