H(t)=−16t2+28t (first 2 is an exponet) the function h(t) gives the approximate height, in feet, of a dolphin's jump out of water, where t represents the time, in seconds. what is the total length of time, in seconds, it took the dolphin to complete one jump? show your work.

It takes 1.75 seconds.

We want to know when the dolphin hits the water again.  We set h(t) = 0 to do this:
0 = -16t² + 28t

We will factor out the GCF:
0 = 4t(-4t+7)

Using the zero product property, we know that either 4t=0 or -4t+7=0:

4t=0
Divide both sides by 4:
4t/4 = 0/4
t = 0

This is when the dolphin first jumps.

-4t+7=0

Subract 7 from both sides:
-4t = -7

Divide both sides by -4:
-4t/-4 = -7/-4
t = 7/4 = 1.75