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Let x represent smaller, y the larger number     
Question States***
 y - x = 45 or
 -x + y = 45 |multiplying thru by 3 to  eliminate the y variable by adding the Eqs
6x - 3y= 75
-3x + 3y = 135
6x - 3y= 75
  3x =210
   x = 70, smaller number, larger 115 