As per your question, total cost of watermelon should end with either 5(for odd quantity) or 0(for even quantity).
If the quantity of watermelon is odd, then the total cost value of pineapple should end with 3 and this is not possible when the cost of pineapple is ₹7.
So let's come to conclusion that the count(quantity) of watermelon should be any one of 0, 2, 4, 6.
If count of watermelon is 6: It will cost ₹30 and for remaining ₹8, we can buy 1 pineapple but still ₹1 will not be utilised. So 1 pineapple is not possible
If count of watermelon is 4: It will cost ₹20 and for remaining ₹18, we can buy 2 pineapple with ₹4 not being utilised. So 2 pineapple is also not possible.
If count of watermelon is 2: It will cost ₹10 and for remaining ₹28, we can buy 4 pineapple with all amount being utilised. We can buy 4 pineapple along with with 2 watermelon for ₹38.
If count of watermelon is 0: It will cost you ₹0 and for remaining ₹38, we can buy 5 pineapple with ₹3 being not utilised. So 5 pineapple is also not possible.
So the answer is 4 pineapple.
