Answer:
9
Explanation:
Perpendicular lines have negative reciprocal slopes. The green line and red line are perpendicular. We know the slope of the green line is -1/9, so we must find the negative reciprocal of -1/9.
Negate
Negate the slope of the green line
-1/9--> 1/9
Reciprocal
To find the reciprocal, flip the numerator and the denominator
1/9--> 9/1
So, the slope of the red line is 9/1, which is equal to 9