Since the circle with centre (α,β) touches the circle x2+(y−1)2=1 externally and also touches x−axis,
therefore the distance between the centres will be equal to the sum of the radius of both circles
i.e. (α−0)2+(β−1)2=β+1
⇒α2=4β
Hence the locus of L will be x2=4y
Now, the area bounded by {x}^{2}=4y&y=4 will be
A=2∫04(4−4x2)dx
=2(4x−12x3)04=364