The time between 8:20 and 7:50 is 30 minutes. If it drops 1°C per minute you multiply this number by the amount of minutes which would be 30. This becomes 30°C. Then add the 3° it's at now to become 33°C.
For three line segments to be able to form any triangle you must be able to take any two sides, add their length and this sum be greater than the remaining side.
