Lets first Consider Option A

The statment says that the faces are 15 and 24.

A rectangular solid has 6 faces with 2 opposite faces.

So the lengts can be 3*5=15 and 3*8=24.

Volume is therefore 3*5*8=120

But the values can also be 1*15=15 and 1*24=24.

Volume there becomes 1*15*24=360.

So Statment A is clearly insufficient.

Option A and D out of the way.

Lets now consider Statment B

The area of two opposite faces is 40.

Therefore the lengts can be 5*8 or 10*4. Again no definte value so insufficient.

Option B out of the way.

Now lets consider both the statements together.

It says the opposite faces are 15 24 and 40.

Therefore the only value that satisfies this condition is the lengths of the solid being 3 5 and 8.

So Volume = l*b*h = 3*5*8=120.

So the answer is C