Question 471156
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Hi,
Robert is now twice as old as Marie
Let x and 2x represent Marie's and Robert's ages NOW
Question states*** 6 yrs ago...
 (x-6) + (2x-6) = 39
Solving for x
           3x = 51
            x = 17, Marie's age now.  Robert is 34  (2*17)
CHECKING our Answer***
   11 + 28 = 39

One side of a triangle is three times the shortest side. 
The third side is 6 inches more than the shortest side. 
Let x, 3x and (x+6) represent the three sides
Question states*** The perimeter of the triangle is 86 inches
  x + 3x + (x+6) = 86in
        5x = 80in
         x = 16in.  Sides are 16in, 48in, 22in  (added up = 86in :)