Answer- (d) None of these

Solution:- Calculate the altitude of the equilateral triangle. Then according to the conditions given,
Diameter of the circle circumscribing the equilateral triangle= Altitude of the equilateral triangle + Diameter of the smaller cirlce.
Solve the above equation for the required answer. 

Alternate Soln: The triangle’s dimension is used to calculate the radii of the outermost and the second circle.

Radius of the bigger circle: R=$\frac{\left(1.5\right)}{cos30}$; =$\sqrt{3}$ units.

Radius of smaller circle:

r = 1.5 tan 30. =  $\frac{\frac{3}{2}}{\sqrt{3}}$ r= $\frac{\sqrt{3}}{2}$.

Radius of smallest circle:

$\frac{\left(\right(radiusofbiggest)-(radiusof{2}^{nd}\left)\right)}{2}$;

= $\frac{\sqrt{3}}{4}$

Hence ans: d (none of these)