Write the meaning of the following business idioms and expressions

i) A rule of thumb: a broadly practical, experience-based principle used for guidance rather than an exact scientific calculation.

ii) Ahead of the game: having a competitive advantage by anticipating trends or acting before others.

iii) Blockbuster: a product — a film, book, or launch — that achieves outstanding commercial success.

iv) Crunch time: a critical, high-pressure period in which important decisions must be made quickly.

v) Multi-task: to handle and perform more than one task or responsibility at the same time.