Suppose you adjust your garden hose nozzle for a hard stream of water. you point the nozzle vertically upward at a height of 1.5 m above the ground. when you quickly turn off the nozzle, you hear the water striking the ground next to you for another 1.8 s .

For problems especially pertaining motion, it is best to illustrate the problem to help you understand the problem. The picture I've attached is my illustration based on what I understood from the problem. Suppose the diamond in the picture is the nozzle. It is placed 1.5 m above the ground (bold horizontal line). The water coming out of the nozzle follows the direction of the arrows until it falls to the ground next to you holding the nozzle. When you turn it off, the water at the topmost part slowly comes back to the ground in 1.8 seconds. 

Unfortunately, you weren't able to complete the problem. However, I would make a smart guess. I think it is logical that the problem would ask how high did the water shoot upwards from the nozzle, denoted as x. In order to solve this, we use the equations for free-falling objects:

t = √2h/g
1.8 = √2h/9.81
h = 15.9 m

To find the height of the water from the nozzle, we subtract the total height to 1.5 m to determine x.

x = 15.9 - 1.5 = 14.4 m

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.