(a) $15 \%$ of what is 30 ?

Step 1 ：Translate the problem into an equation: \(0.15 * x = 30\)

Step 2 ：Solve the equation for x: \(x = \frac{30}{0.15}\)

Step 3 ：Calculate the value of x: \(x = 200\)

Step 4 ：Final Answer: \(\boxed{200}\)