In a rectangular park of dimensions 50 m * 40 m a rectangular pond is constructed so that the area of grass strip of uniform with surrounding the point would be 1184 m square find the length and breadth of the pond

     see the attached picture to better understand the problem

we have that
dimensions of rectangular park = 50 m x 40 m
So
 Area of park = 50*40 = 2000 m²
Area of the grass strip surrounding the pond = 1184 m²
Hence,
area of the pond = 2000-1184 = 816 m²                   
Let
x--------> the width of the grass strip 
So,
 (50-2x)(40-2x) = 816
⇒ 2000 - 100x - 80x + 4x² = 816
⇒ 2000-180x+4x² = 816⇒4x²-180x+1184 = 0
⇒x²-45x+296 = 0
⇒x²-37x-8x+296=0

using a graph tool
see the attached figure N 2

the solution is 
x=8
Width of the grass strip = 8 m

Length of the pond = 50-16 = 34 m
Breadth of the pond = 40-16 = 24 m