Question 729602
(2,a) and (5,-3)

slope {{{m= (-3-a)/(5-2)}}}

=(-3-a)/2

 is parallel to the line passing through the points 

(4,8) and (-5,a+1)

slope {{{m= (a+1-8)/(-5-4)}}}

={{{(a-7)/-9}}}

the lines are parallel so the slopes are equal


{{{(-3-a)/2  = (a-7)/-9}}}

-9(-3-a)=2(a-7)

27+9a=2a-14

7a=-41

a=-41/7