Question 2275
 
  perimeter(p) = 2l + 2b = 2(l+b)

  Let the width be = x cm
 
  So length = x + 5 cms.
 
  By applying the above formula, 
 
  40 cms = 2(x+x+5)
 
  20 cms = x+x+5 = 2x+5
 
  2x = 20-5 = 15
 
  x = {{{15/2}}} = 7.5 cms.
 
  So width = 7.5 cms.;  length = 7.5+5 = 12.5 cms.  Ans.