Answer:
Her oven will cool to 75°F in 100 minutes, or 1 hour 40 minutes.
Step-by-step explanation:
Let T(t) represent the oven temperature, and t the time in minutes.
Then:
T(t) = 400°F - (3.25°F/min)t
Find the time, t, at which T(t) will = 75°F:
400°F - (3.25°F/min)t = 75°F
Subtracting 75°F from both sides, we get:
(3.25°F/min)t = 325°F.
Dividing both sides by (3.25°F/min) yields:
t = 100 minutes.
Her oven will cool to 75°F in 100 minutes, or 1 hour 40 minutes.