(c) $10 \%$ of what is $\$ 15$ ?

Step 1 ：We need to find a number such that 10% of it is equal to $15. This can be represented as an equation: \(0.10 * x = 15\).

Step 2 ：We can solve this equation for x to find the answer.

Step 3 ：\(x = 150.0\)

Step 4 ：Final Answer: \(10 \%\) of \(150\) is \(\$ 15\). So, the answer is \(\boxed{150}\).