To translate into math, the question is asking you "for what approximate t value does h = 0?" In order to solve, you can plug in 0 for h and solve for t.
0 = -16t^2 + 620
-620 = -16t^2
620 = 16t^2
38.75 = t^2
= t
6.2 ~~ t (rounding to the nearest tenth)
Don't forget your units!
Let me know if you need anything explained in more detail; I'm happy to help.
Diameter = 2*radius 14/2=7 Radius is 7in" Circumference of circle formula: 2pi(radius) 2pi(7)= 43.98in of wire required so it can wrap around lamp exactly once.