7. In the Magic Land, there is a magic stone that grows uniformly upwards. To prevent it from piercing the sky, the Elders of the Immortal World decided to send plant warriors to consume the magic stone and suppress its growth. Each plant warrior consumes the same amount every day. If 14 plant warriors are dispatched, the magic stone will pierce the sky after 16 days; if 15 plant warriors are dispatched, the magic stone will pierce the sky after 24 days. At least $\qquad$ plant warriors need to be dispatched to ensure the sky is not pierced.
【Analysis】Assume 1 plant warrior consumes "1" unit of magic stone per day.
Then, 14 warriors consume $14 \times 16=224$ units in 16 days.
15 warriors consume $15 \times 24=360$ units in 24 days.
The additional consumption is 136 units, which grew in 8 days, so the magic stone grows $136 \div 8=17$ units per day.
Therefore, at least 17 plant warriors need to be dispatched to ensure that the daily growth of the magic stone does not exceed the amount consumed, i.e., the growth of the magic stone is suppressed, and the sky will not be pierced.