The function f(t) = -18t2 + 42t + 36 represents the height of the path traced by an airborne flying disc, where t is the time in seconds. how many seconds will it take the flying disc to complete its path?

To complete path means the disc lands on the ground, the height f(t)=0
-18t²+42t+36=0
simplify by dividing -6: 3t²-7t-6=0
facotor: (t-3)(3t+2)=0
t=3 or t=-2/3 (discard this negative one because time cannot be negative. 
so the answer is 3 seconds. 

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2