Neena purchased two oranges, three bananas and four apples which cost her Rs. 15.
Had Neena purchased three oranges, two bananas and one apple, it would have cost her only Rs. 10.
If Neeena bought 3 oranges, 3 bananas and 3 apples, determine as to how much did she have to pay ?

Let: 

Cost of one orange = O
Cost of one banana = B
Cost of one apple = A

We are given that:

2O + 3B + 4A = 15...(1)

3O + 2B + A = 10...(2)

Now, we need 3O + 3B + 3A = 3(O + B + A)

Now, we will aim to eliminate the variables. 

Multiply (2) by 4: 12O + 8B + 4A = 40...(3)

Subtract (1) from (3): (12O - 2O) + (8B - 3B) + (4A - 4A) = 40 - 15 

We get: 10O + 5B = 25

Or, 2O + B = 5...(4)

Now, From (4): B = 5 - 2O

Substitute into (2): 3O + 2(5  - 2O) + A = 10
3O + 10 - 4O + A = 10
-A + O + 10 = 10
A = O

We need to find O + B + A.

O + B + A = O + (5 - 2O) + O = 5

Final value 3(O + B + A) = 3 × 5 = 15