Cast Is off!

Hey everybody!
My cast is now off : ) I'm happy about that but....I asked when I can start riding again. The doctor said MAYBE after I see him next. In two months! At this rate I won't be able to ride til my birthday in February! grrrr And right now I'm trying to do online work my algebra 2 teacher assigned...grrr i'm not doing good at all.
Here is one question.
After an oven is turned on, its temperature, T, is represented by the equation T = 400 - 350^(3.2)-0.1m, where m represents the number of minutes after the oven is turned on and T represents the temperature of the oven, in degrees Fahrenheit.
How many minutes does it take for the oven’s temperature to reach 300°F? Round your answer to the nearest minute.
I have no idea of how to do this and the website will lock me out of it when 12 comes around! ahhhh!!!