Which property states that a(b + c) = ab + ac?

Hey there :)

a ( b + c ) = ab + ac

The Distributive property will be your answer. 
This is when you are multiplying a term outside by terms that are inside the parenthesis.

38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)