Use Factor-Label Method:
8miles 63360 inches
---------- X --------------------- X
1 1 mile
2.54cm 1 meter
X ------------ X ---------------- X
1 inch 100 cm
1 km
----------------- = 12.87 km
1000meters
8 miles = 12.87 km
C.) In this, number of Hydrogen atoms is 4
A) Up is the direction of the magnetic field at point Z.
The answer is centimeters.