Explanation

Find the value of "a"

a + 4 = 10 

a = 10 - 4 

a = 6 

__

Find the value of "b"

b + 10 = 4 

b = 4 - 10 

b = - 6 

find :

a + b = 6 + ( - 6)

= 6 - 6 

= 0