1. State the problem: Simplify and factorise the expression b) $3x^2 - 11 + x^2 - 7$. 2. Formula and rules: Combine like terms by adding coefficients of the same power, e.g. $ax^n + bx^n = (a+b)x^n$. 3. Combine like terms step-by-step. $$3x^2 - 11 + x^2 - 7 = (3x^2 + x^2) + (-11 - 7)$$ $$= 4x^2 - 18$$ 4. Factorise by extracting the greatest common factor. $$4x^2 - 18 = 2\left(\frac{2\cdot 2x^2}{2} - \frac{2\cdot 9}{2}\right)$$ $$= 2\left(\frac{\cancel{2}\cdot 2x^2}{\cancel{2}} - \frac{\cancel{2}\cdot 9}{\cancel{2}}\right)$$ $$= 2(2x^2 - 9)$$ 5. Final answer: The simplified expression is $4x^2 - 18$ and its factorised form is $2(2x^2 - 9)$.