21. D. is the answer. Angle Q is 75 degrees. X=30. The triangle is an isosceles angle so therefore there are 2 angles are congruent to each other, Angle R and Angle Q. All three of the angles should add to 180 degrees.
To be honest my example for this is 160
The domain is the limits of the function. Since time doesnt go negative, start with 0. At time 0, the height is
-16(0)^2 + 144 = 144ft
Then, solve for t to find the upper limit for t, which is when the height is zero (since you're dropping the object).
-16t^2 + 144 = 0
-16t^2 = -144
t^2 = 9
t = sqrt(9)
t = 3
The domain is 0 to 3 seconds.
Breaking the it down- simplifying
