71-5= 66
71-66=5
The temperature needs to rise 5 degrees for the temperature to return to 71 degrees.
A stuntman jumping off a 20-m-high building is modeled by the equation h = 20 – 5t2, where t is the time in seconds. A high-speed camera is ready to film him between 15 m and 10 m above the ground. For which interval of time should the camera film him?
Answer:

Step-by-step explanation:
Given:
A stuntman jumping off a 20-m-high building is modeled by the equation
-----------(1)
A high-speed camera is ready to making film between 15 m and 10 m above the ground
when the stuntman is 15m above the ground.
height
Put height value in equation 1





We know that the time is always positive, therefore 
when the stuntman is 10m above the ground.
height
Put height value in equation 1







Therefore ,time interval of camera film him is 
Use the FOIL method (First, Outside, Inside, Last)
6r(-8r) = -48r²
6r(-3) = -18r
-1(-8r) = 8r (note: two negatives multiplied together = positive answer)
-1(-3) = 3
-48r² - 18r + 8r + 3
Combine like terms:
-48r² - 18r + 8r + 3
-48r² - 10r + 3
-48r² - 10r + 3 is your answer
hope this helps
Any number times 0 is going to equal 0