Question 925562
Let width be w  cm
length  = (w+3) cm
diagonal  = 15 cm
as per pythagorean theorem 
          {{{ w^2 +(w+3)^2 =15^2}}}
             {{{ w^2+ (w+3)*(w+3) = 225}}}
              {{{ w^2 +w*(w+3)+3(w+3) =225}}}
                {{{ w^2 +w*w+w*3+ 3*w+3*3  =225}}}
            {{{ w^2 +w^2 +3w+3w+9 =225}}}
              {{{ 2w^2+6w+9 =225}}}
           move 225 to the right
            {{{ 2w^2+6w+9-225 =0}}}
          {{{ 2w^2+6w-216=0}}}
             on dividing with 2 both sides
                 {{{ w^2 +3w-108=0}}}
                 {{{ w^2+12w-9w-108=0}}}
                  {{{ w(w+12)-9(w+12) =0}}}
                {{{ (w-9)(w+12)  =0 }}}
                (w-9) =0 or (w+12 )= 0
                w=9       or w=-12
           w cannot be negative
so w= 9
  l = w+3 = 12
so length  = 12 cm
 width  = 9 cm