Let's define the next variable:
t: number of toys that Quinn still needs to collect
The number of toys that he already collected plus the number of toys that Quinn still needs to collect is: 16 + t
Quinn needs to collect at least 90 toys, then 16 + t must be greater than or equal to 90, that is,
16 + t ≥ 90
or
90 ≤ 16 + t
Subtracting 16 at both sides, we get:
90 - 16 ≤ 16 + t - 16
74 ≤ t
