In an art lesson at Tampines Primary, Mrs Lee uses the formula $A = (3x - 5)(x + 2)$ to estimate the area, in square centimetres, of a rectangular canvas, where $x$ is a size code. Find the value of $A$ when $x = 4$.
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Worked Solution
Step 1: Substitute x = 4 into the first bracket: 3x − 5 = 3(4) − 5 = 12 − 5 = 7.\n
Step 2: Substitute x = 4 into the second bracket: x + 2 = 4 + 2 = 6.\n
Step 3: The expression (3x − 5)(x + 2) means the two brackets are multiplied: 7 × 6 = 42.\n
Step 4: A = 42 square centimetres.
Answer: 42
Correct answer: 42
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