opensof,

Your interpretation is correct. The $10.50 is before tax.

opensof,

Your interpretation is correct. The $10.50 is before tax.

Then how is it that both together are not sufficient?

As I see it:

number of books (n): 10 (at least, as it says n>9)
unitary price: $10.50 (before tax*)

Then, minimum total revenue=10*10.50=$105 > $100

For me that would mean that BOTH statements together are required

It is not important to know whether $10.50 includes tax cos you don't know the tax rate.
The Q is to find the revenue minus the tax. So E

Yeah, the ans should be C.

Yes, the ans. should be 'C',

Since the Question asks abt exclusive tax and the stmt 2. also provide exclusive tax.

So by combining stmt 1 and 2, we have the result exclusive tax.

So, 'C' is my best bet.

is 105- tax > 100 ?

tax is unknown.

The question asks if the revenue, excluding the tax is >100 or not
Yes/ No question

So,
From stmt1. we have no clue of how much each book cost.

From stmt2. we know the price of each book excluding tax.

But combining both the stmts we know the revenue excluding tax.

Since, it is a DS question we don't need the value/ the revenue (In numbers)

So, my strong bet would be 'C'.