write the missing numbers to.make the sentence true example 7+9=_______+7?

Answer 1

make a guess and I will come back and look

Answer 2

if 7 cows + 9 cows fill a field
then
9 cows + how many cows
fill the field?

Answer 3

ah, here we go:

http://coolmath.com/prealgebra/06-properties/01-properties-commutative-addition-01.htm