Problem: four horses are tethered at four corners of a square plot of side 63 metres so that they just can not reach one another . the area left ungrazed is : 
Options: ['a ) 675.5 m 2', 'b ) 780.6 m 2', 'c ) 785.8 m 2', 'd ) 850.5 m 2', 'e ) 950.5 m 2']
d