Hi,
the line passing through points (x,4)and(4,-5) is perpendicular to a line with a slope of -7/3
Note: Perpendicular lines have slopes that are the negative reciprocal of one another
Using the point-slope formula, 
(x, 4)and
(4,-5) m =
|| m = 3/7 the slope of the perpendicular line
Cross Multiplying to solve:
3(x-4) = 63
3x-12 = 63
3x = 75
x = 25
CHECKING our Answer***
(25, 4)and
(4,-5) m = 9/21 = 3/7