Statement 1 => In year x counterfeit cards, telephone and mail-order fraud accounted for 39% of the total amount that card fraud cost the banks

Let the total amount of credit-card frauds cost = x
Counterfeit cards + telephone + mail order fraud = 39% of x
This cannot give us the exact value of x hence credit-card frauds cannot be estimated to the nearest 10 million. Statement 1 is NOT SUFFICIENT

Statement 2 => In year x, stolen cards accounted for $158.4 million or 16% of the total amount that credit card fraud cost the banks
Let the total amount of credit card frauds cost = x
Stolen cards = $158.4 million
$158.4 million = 16% of x
$$$158.4\ million\ =\ \frac{16}{100}\cdot x$$
$$x=$158.4\ million\ \cdot\ \frac{100}{16}$$
$$x=9.9\ million\ \cdot\ 100$$
$$x=9,900,000\cdot100$$
$$x=990,000,000$$
$$x\approx990.0\ million$$

Statement 2 alone is SUFFICIENT
Answer = B