Suppose a scientist finds that the average female gorilla needs to have at least 2.1 surviving offspring in order for the population, to replace itsself from generation to generation.

how would she write an inequality of offspring (c) that will cause the population to decrease from generation to generation.

The scientist can write the inequality as c < 2.1. This means that if the average female gorilla has less than 2.1 surviving offspring, the population will decrease from generation to generation.