Aroast turkey is taken from an oven when its temperature has reached 185°f and is placed on a table in a room where the temperature is 75°f. the graph shows how the temperature of the turkey decreases and eventually approaches room temperature. by measuring the slope of the tangent, estimate the rate of change of the temperature after an hour.

Vertical lines are 50º apart. Horizontal lines are 30 minutes apart.

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