Solve the Diffeq to get:
T(t) = Tₐ + (T₀ - Tₐ)∙e^(-kt)
T₀ is the initial temperature of the object = 185°F
Tₐ is the ambient temperature = 75°F
Unfortunately, you have not been given enough information to solve this problem. You'll need a k-value for turkey in order to solve this or another equation in which you can solve for k.
If you assume k ≈ 0.4 like this question (see below), then:
90 = 75 + 110∙e^(-0.4t)
t ≈ 4.98 minutes
It depends on what unit of k had
