H=-16t^2+56t+1, the airplane is shot up from a platform 1 foot above the ground, so 1= - 16t^2+56t+1, we solve this equation
(- 16t+56)t=0, (- 16t+56)=0 or t=o, - 16t+56=0, implies t =3.5s
so the answer is C)3.5 seconds
Answer:
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Answer:

Step-by-step explanation:
Given
← factor numerator and denominator
=
← cancel common factor (x + 1) on numerator/ denominator
= 
[ Answer ]

[ Explanation ]
Area = 1420
Width = 
Area For Rectangle: Length · Width
Use division to find width:
1420 ÷ 
Convert mixed numbers to fractions:
1420 = 
= 
÷ 
Use mixed multiplication:

= 
Simplify:
= 
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The radius is half the diameter, so the formula would be r=d divided by 2