Can the hypotenuse or a leg be a decimal? Why or why not?

Could somebody me with this radical simplification?

What is the best approximation for the area of a circle with a radius of 4 m ? use 3.14 to approximate pi

Asales representative from a local radio station is trying to convince the owner of a small fitness club to advertise on her station. the representative says that if the owner begins advertising on the station today, the club's total number of members will grow exponentially each month. she uses the given expression to model the number of club members, in hundreds, after advertising for t months.