Find the missing side length

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

The graph below shows the height of a projectile t seconds after it is launched. if acceleration due to gravity is -16 ft/s2, which equation models the height of the projectile correctly?