Question

The area of a square feild is 8hec how long a man woul tahe to cross its diagonol by walking at the rate of 4km/hr

Answer 1

The symbol of hectare is ha, no "hec".
1 ha = 100 m · 100 m = 10000 m²

Because the area is a square, the side of it is √A, where A=8 ha = 80000 m²
a = √A = √(80000) = √8√10000 = 100√8 [m]

The length of diagonal d of square with side a is a√2, so:
d = 100√8√2 = 100√16 = 100 · 4 = 400 m = 0.4 km

Time of walking along of diagonal:
$t=\frac{d}v=\frac{0.4}{4}=0.1\ h=0.1\cdot60\ \min=6\ \min$