My brother needs help with this !

0if x and y vary inversely and y=6 as x=7, what is the constant of variation?

Find the perimeter of the triangle with vertices  d(3, 4),  e(8, 7), and  f(5, 9). do not round before calculating the perimeter. after calculating the perimeter, round your answer to the nearest tenth.  

Present age of man is 45 years, 5 years back his age was 4 times age of his son what is present age of his son?