Simplify sqrt(64+64x²) = sqrt(25+25x²)

The question paper of an examination comprises three sections of 7, 6 and 5 questions respectively. A total of 15 questions are to be answered, with a minimum of three questions to be answered in each section. Also the number of questions answered from the second section shall be more than those answered from each of the remaining two sections. In how many different ways can a candidate choose to answer the required total of 15 questions from among the three sections?

The average of five different positive numbers is 25. x is the decrease in the average when the smallest number among them is replaced by 0. What can be said about x?