Circle A in the $xy$-plane has the equation $(x-7{)}^2+(y+3{)}^2=25$. Circle B has the same center as circle A. The circumference of circle B is four times the circumference of circle A. The equation defining circle B in the $xy$-plane is $(x-7{)}^2+(y+3{)}^2=k$, where $k$ is a constant. What is the value of $k$?