The Three Tier Spell Silent Field would require eight hours of study, and once mastered, it could reduce the Sixteen hours needed to learn the Fifth Tier Spell High-level Silence Field by half.
Zhang Yanhang did some calculations and realized that if he finished studying both prerequisite spells, the learning time for the Fifth Tier Spell High-level Silence Field would be reduced to just 39 hours, saving 19 hours from the original estimate.
Even if you subtract the 9.5 hours required to learn the Zero Ring Illusion Sound Barrier and the Three Tier Spell Silent Field, you'd still save an extra 9.5 hours. Therefore, it was profitable overall to learn the prerequisite spells before tackling the Fifth Tier Spell High-level Silence Field.
