Concept:The product is the result of multiplying the three numbers. Let the unknown number be x and form an equation.Given:Product = 90, two numbers are 6 and 3.Solution:6×3×x=90Multiply the known numbers: 6×3=18, so 18x=90Divide both sides by 18:x=1890=5Check: 6×3×5=90 ✓.Answer:Option D (5)