Explanation:
Here, slope of the line (m) = 1
Here, slope of the line (m) = 1And, the line passes through the point (7,9)
Equation of the line is given by 
y - y1 = m ( x - x1 )
y - 9 = 1( x - 7)
y - 9 = x -7
x -7+9-y = 0
x - y + 2 = 0 
                 is the required equation of the line.