Let

*d*_{1},

*d*_{2},

*d*_{3} and

*d*_{4} be the distances travelled and

*s*_{1},

*s*_{2},

*s*_{3} and

*s*_{4} be the speeds in 1

^{st}, 2

^{nd}, 3

^{rd} and 4

^{th} hours respectively.

At the end of three hours distance travelled by the farmer is

*d*_{1} +

*d*_{2} +

*d*_{3} = 0.7

*d* (where

*d* is the distance between his house and village temple)

Let

*x* be the original speed (in km/hr) of the farmer.

Now, to reach the village temple in time the farmer has to travel the distance of 0.3

*d* in one hour.

∴ Percentage increase in the speed in the fourth hour (as compared to his speed third hour)

≈ 71.42%

Hence, option 4.