I think that x=2 and so does y=2. Hope that answers your question.
This is a linear programming question
if u want to solve the question, u can plot a graph(see the picture)
while x is n, y is r
and u may find out all of the integral values of x ,y in the required region, and sub them to 6450x+7150y=c, where c is the overall customers number, see which point give u the largest number of customers, u may get the ans then
We can solve this equation by completing the square. Notice that

and

. Therefore, we can turn

into

. y, in this equation, only has one real solution: 4. So your answer would be (B).
Pythagorean theorem formula is a^2 + b^2 = c^2
7^2 + 11^2 = 170
You will get the value of c by square-rooting 170
Therefore, the answer is √170
21-3= 18 and 18 divided by 6 equals 3 so v=3