The object is in air for 3.5 seconds.

Step-by-step explanation

The movement of the object is described by the equation

h(t)=−4.9t2+17t

where h is the height in meters and 

t is the time in seconds.

We are asked how long is the object in air. Take note that when an object is thrown up, it will remain in air until it falls down and reaches the ground, and when it reaches the ground, h(t)=0.

0=−4.9t2+17t

4.9t2=17t

4.9t=17

t=4.917?

t=3.5 seconds 

The object is in air for 3.5 seconds.