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Whats the name of the vertical axis

An airplane travels at an unknown elevation before it descends 3 miles to an elevation of 15 miles. find the elevation of the plane before its descen.

Write the equation of the line that passes through (3, 4) and (2, −1) in slope-intercept form. (2 points) y = 3x − 7 y = 3x − 5 y = 5x − 11 y = 5x − 9