She can buy 3 tubes be cause 8.50 time 2 is less then 20$ but 8.50 times three is more than 20$ its 25.5
Answer:
Step-by-step explanation:

Auxialary equation is

General solution is



Eliminate B to get
3A =a-1
We know that y tends to 0 when x tends to infinity for any finite A
i.e. a should be a finite real number.
Im not sure but i think its 1.22474487
sorry just in case its wrong :(