Step 1 :Let's represent the unknown number as 'x'.
Step 2 :Translate the given condition into the equation: \(0.5x = 3(x + 5)\).
Step 3 :Solve this equation to find the value of 'x'.
Step 4 :The solution to the equation is -6.
Step 5 :This means that the number that satisfies the given condition is -6.
Step 6 :Final Answer: \(\boxed{-6}\)