Answer:
The statements are not provided, so i will answer in a general way.
Let's define the variable x as the number of dress shirts brought for some person.
In store A, each one costs $15.
Then the cost of x dress shirts will be:
A(x) = $15*x.
In store B, each one costs $18, but there is a coupon of $9, then we can write the cost in store B as:
B(x) = $18*x - $9.
Now we can find wich store will be cheaper for a given number x, by calculating the difference between A(x) and B(x).
D = A(x) - B(x)
If D is positive, means that B(x) is cheaper.
If D is negative, means that A(x) is cheaper.
If D is equal to zero, means that the cost is the same in both stores.
D = A(x) - B(x) = $15*x - $18*x + $9 = (-$3*x) + $9.
First, let's find for what value of x we have the same cost in both stores:
0 = (-$3*x) + $9.
$9/$3 = 3 = x.
Then for 3 dress shirts, the cost will be the same in each store.
Now, as the coefficient that multiplies x is negative, if we have x > 3, then D will be negative, and if x < 3, D will be positive.
then:
For x = 3, the cost is the same in both stores.
for x > 3, Store A is cheaper.
For x < 2, Store B is cheaper.
