<h2>
Answer:</h2>
The example of a function is:
The price of a piece of cloth and the length of the cloth.
<h2>
Step-by-step explanation:</h2>
We know that a function is a relation in which each element of a set is mapped to a single element of the other set.
i.e. an element has just one image.
1)
The time it takes to mow a lawn and the age of the person mowing the lawn.
This is not a example of function since, the time taken by two person's of different age may be same to mow a lawn.
This means that there is more than one image of a single element i.e. time.
2)
The distance to school and the time you spend at school.
The time one spend at school at different days may be different even if the distance to school is same.
3)
The price of a movie ticket and the height of the customer.
Two person's with different height will buy a movie ticket at the same cost.
Hence, this relation won't be a function.
4)
The price of a piece of cloth and the length of the cloth.
As we know that the price of a cloth is fixed according to the length.
Hence, the relation is a function.
( As corresponding to each price we have a unique length if a piece of clothing )
, the discriminant is given by 
.
, then the quadratic has two distinct real roots. If 
, then there is one repeated real root. If 
, then there are two complex (non-real) roots.
, that means that 
has two distinct real roots.