Теория:

As one amount increases, another amount increases at the same rate or as one amount decreases, and another amount decreases at the same rate is known as direct proportional.
The symbol for "directly proportional" is α.
Example:
You are paid  \(₹\)30 an hour. How much you earn is direct proportional to how many hours you work.
Work more hours, get more pay; in direct proportion. 
This could be written:
 
Earnings α Hours worked
 
If you work for 1 hour, you get paid \(₹\)10.
If you work for 4 hours, you get paid \(₹\)40.
If you work for 7 hours, you get paid \(₹\)70.