1. The problem is to find a simple formula for expanding a bracket multiplied by 3. 2. When you have an expression like $3(a + b)$, the distributive property of multiplication over addition applies. 3. The formula is: $$3(a + b) = 3 \times a + 3 \times b$$ 4. This means you multiply each term inside the bracket by 3. 5. For example, if you have $3(x + 5)$, it expands to $3x + 15$. 6. This rule works for any number of terms inside the bracket: $$3(a + b + c + \dots) = 3a + 3b + 3c + \dots$$ 7. So, the simple formula for expanding a bracket by the multiple of 3 is to multiply each term inside the bracket by 3 and then add the results.