Answer:
7 seconds
Step-by-step explanation:
Distance of the coin above the water is modeled by the equation

where
is time taken to cover the distance
Now equating with zero.

So, time taken by the coin to hit the water is 7 seconds.
To make that graph you follow these steps.
1) Set the cartesian coordinate system:
- vertical axis: y
- horizontal axis: x
- positive x-semi axis: to the right
- negative x-semi axis: to the left
- positive y-semi axis: upward
- negative y semi axis: dwonward
2) solve the inequality for y:
given: -2x + 5y > 15
transpose-2x: 5y > 15 + 2x
divide by 5: y > 3 + (2/5)x
3) Graph-
draw the line y = 3 + (2/5)x, using a dotted line (i.e. - - - - - -)
- remember that 3 is the y intercept, and 2/5 is the slope
- the line is dotted because
the solution does not include the points in the line.
- the solution is the
region above and to the left of the dotted line.
4) See the
figure attached for better visualization: the pink region is the solution of the inequality.