Is 721 ft above sea level

Yes

Step-by-step explanation:

Because f all of the Earth's ice sheets and glaciers were to melt, sea level could be up to 265 feet (80 meters) above current mean sea level.

y = 7

Step-by-step explanation:

x=4 is a vertical line that goes through the point x=4. y value of this graph changes while x value will be 4 at every point of the graph.

A line perpendicular to this will be a horizontal line with a fixed y value and the x value will change.

The coordinates of the point of which the line has to pass is given as (5,7). Which means the y coordinate of this line is 7.

As we have established that this line has to have same y value at each point just like x=4 has same x value at each point, we can say the equation of the line is y=7.