Explanation:
Simplifying
(2a2b4z)(6a3b2z5)
Remove parenthesis around (2a2b4z)
2a2b4z(6a3b2z5)
Remove parenthesis around (6a3b2z5)
2a2b4z * 6a3b2z5
Reorder the terms for easier multiplication:
2 * 6a2b4z * a3b2z5
Multiply 2 * 6
12a2b4z * a3b2z5
Multiply a2b4z * a3b2z5
12a5b6z6