The equation of a circle is given by:

where (h,k) is the center and r is the radius.
In this case we know that the center of the circle is (-4,3). To find the radius we just need to remember that the radius is half the diameter, hence:

Plugging the values for the center and the radius we have that:

Therefore, the equation of the circle is:
![\operatorname{\lparen}x+4)\placeholder{⬚}^2+\left(y-3\right)^2=(81)/(4)]()