With this information, we can find a system of inequalities. Remember that "at least" means that the sum of these number is 30 or more, and their difference is 10 or more. So
The solution of this system is attached. Remember that the solution of a system of inequalities is a graphic solutions, the intersection of all three areas is the solution.
However, the problem is just asking for the system that could represent this situation. So, the answer is
Well the answer would be $18.8784 but if you want it to be shorter it would be $18.88 because you multiply 17.48 and 0.08 and get 1.3984 and then you add it to $17.48