Answer :
Slope formula: (y2-y1)/(x2-x1)
(5-f)/(-10-(-9)) = 3
(5-f)/(-1) = 3
5 - f = -3
-f = -8, f = 8
Solution: f = 8
(5-f)/(-10-(-9)) = 3
(5-f)/(-1) = 3
5 - f = -3
-f = -8, f = 8
Solution: f = 8