Engineers are designing a rollercoaster that at one point goes underground. The rollercoaster's path underground is a large curve. The engineers use the function shown to model the elevation, E, in feet and T, time, in seconds, of the rollercoaster's path while it is underground.

E(t)= t^2-10t+16

Part A: Write a equivalent form of E(t) that can be used to find the time when the rollercoaster goes underground and the time the rollercoaster returns above ground.

E(t)=________________

Part B: How long, in seconds, was the rollercoaster underground?