What is the value of x in the following proportion? 7/x-5 = 15/x+4

For this question you should first add -15/x on both sides of the equation and then add +5 on both sides:
7/x - 15/x = 5 + 4 
-8/x = 9 
so now you can multiply both sides by x:
-8 = 9x 
now you should divide both sides by 9:
-8/9 = x :)))
I hope this is helpful
have a nice day