Fill in the blank space

z2 + 5z - 36 = (z - 4) (z + _)

Answer=9

To solve this, we just have to find a number that, when added to - 4, make a total of 5, and when multiplied by - 4 make a total of - 36.

x+-4=5

x*-4=-36

9 fits the parameters for both of these

9+-4=9

9-4=5

5=5

9*-4=36

36=36