Someone please help I have no idea

What properties allow transformation to be used as a problem solving tool

Me. i can't figure out this question. give an explanation too. .

Prove the divisibility of the following numbers: 25^9 + 5^7 is divisible by 30.also, read as (25 to the power of 9) + (5 to the power of 7) is divisible by 30. blank x 30what is the blank? ( it should be expressed in exponent form)