Here is the work and the answer (D=7
We will make use of the concept of prime factors for solving this question. The prime factors of 1517 are:

So, as can be clearly seen the Niagara Fall tour operator can either sell 37 tickets for $41 each or 41 tickets for $37 each.
Now, we know that we cannot reach $37 using just three bills. Thus, the only option left to us is $41 which can be broken down into three bills of $20,$20 and $1. This satisfies our condition.
Thus the cost of a ticket was $41 and 37 such tickets were sold.
Answer: 28.6
Step-by-step explanation:
Solve for A:3 + 5/a = 3/A - 2
3 + 5/a = 3/A - 2 is equivalent to 3/A - 2 = 3 + 5/a:3/A - 2 = 3 + 5/a
Bring 3/A - 2 together using the common denominator A:(3 - 2 A)/A = 3 + 5/a
Multiply both sides by A:3 - 2 A = A (3 + 5/a)
Subtract (3 + 5/a) A + 3 from both sides:A (-5/a - 5) = -3
Divide both sides by -5/a - 5:Answer: A = 3/(5 + 5/a)