To determine the height of the rock at a specific time, we need to substitute the time value into the equation y = 20t - 1.87t². For example, to find the height of the rock after 3 seconds, we substitute t = 3 into the equation:
y = 20(3) - 1.87(3)²
y = 60 - 16.83
y = 43.17
Therefore, the height of the rock after 3 seconds is 43.17 meters.