Divyansh,

If I drive my car at 110 kph the the relationship between the distance I travel d and the time it takes t is d = 110 × t. A straight line.

When I am at the market and see the price of a vegetable in dollars per kilogram, I weigh the vegetables and calculate the cost using cost in dollars equals cost per kilogram times the weight in kilograms. A straight line.

If I measure a piece of cloth and it is 235 mm long and the price is in metres then I calculate the length in metres by length in metres = 1/100 × length in millimeters. A straight line.

I am in Canada and you are in India and I am sure we both have to deal with the Imperial system of weights and measures some times. I know there are 2.54 cm in an inch so converting one to the other is either multiplying or dividing by 2.54. Again a linear function.

The common temperature units don't even have the same zero but the relationship is linear, F = 9/5 C + 32.

I hope this helps,
Penny