Question

do it fast with complete explanation

Answer 1

dude radius = 1/2of diameter 
r= 1/2d 
so area of circle= πr²
putting value of r we get 
A= π(d/2)²= π/4 d² dude have any doubt ask in comment box 

Answer 2

diameter = d
radius= d÷2
area of circle=  π(r)²

 π(d/2)²
π(d²/4)
thts say
b is correct