Distribute the monomial to each of the terms of the trinomial by multiplication:
4ab(5a2b2+2ab-3)=20a3b3+8a2b2-12ab. Use arithmetic multiplication for pure numbers and algebraic multiplication of algebraic literals, which means adding exponents for like literals. For example, 4ab times 5a2b2. 4×5=20 (pure number); a×a2=a3; b×b2=b3. Now combine these 20a3b3.