Answer:
m + c = - 4.4
Step-by-step explanation:
Line 1 is given by the equation 5x + 8y = -9, ⇒
........(1) {In slope-intercept form}
If line 2 is perpendicular to the line 1 then the equation of line 2 will be
........ (2), where c is a constant. {Since the product of the slopes of two perpendicular straight line is -1}
Now, the line 2 passes through the point (10,10).
So, from equation (2), we get,

Therefore, the equation of line 2 will be 
This equation is in y = mx + c form where
and c = - 6
Hence, m + c = 1.6 - 6 = - 4.4 (Answer)