The first,second and third term of the proportion are 42,36,35 find the forth term

There is something known as the Law of Exponents. There are many forms of it, but we are using only 2 of them, the Product Rule and the Quotient Rule. The Product Rule indicates that x^a*x^b=x^a+b. The Quotient Rule indicates that x^a/x^b=x^a-b. Solution A is correct because 5^5*5^7/5^13 = 5^5+7-13=5^-1 or 1/5. Solution B is correct because 5^5+7+(-13) = 5^-1 or 1/5. Solution C is correct because 5^12-13=5^-1 or 1/5. Solution D is correct because 5^5+7-13=5^-1 or 1/5. If you are confused at all, don't hesitate to ask questions.