What 2 numbers multiply to get -216 and add together to get 6

One No. = x 
Other No. = y 

xy = 6 Eq. 1 

x + y = - 5, or 
y = - x - 5 Eq. 2 

Subbing (- x - 5) from Eq. 2 
for y in Eq. 1, 

x(- x - 5) = 6 
- x² - 5x = 6 
x² + 5x = - 6 
x² + 5x + 6 = 0 
(x + 2)(x + 3) = 0 

If the product of two factors equals zero, 
then one or both factors equal zero. 

If x + 2 = 0, 
x = - 2 

If x + 3 = 0, 
x = - 3 

The two numbers are - 2 and - 3.