1. **State the problem:** Factorise the expression $pm + 3p - m - 3$. 2. **Recall the factoring method:** We can use grouping to factorise expressions with four terms. Group terms to find common factors. 3. **Group terms:** Group the first two and last two terms: $$pm + 3p - m - 3 = (pm + 3p) - (m + 3)$$ 4. **Factor out common factors in each group:** $$p(m + 3) - 1(m + 3)$$ 5. **Factor out the common binomial factor:** $$\cancel{(m + 3)}(p - \cancel{1}) = (m + 3)(p - 1)$$ 6. **Final answer:** The factorised form is $$(m + 3)(p - 1)$$.