The area of a square is given by the function $a(x)=x^{2},$ where $x$ is the length of the sides of the square, If carpeting costs $\$ 9.95$ per square yard, then the cost $C(a)$ (in dollars) to carpet a square room is given by $C(a)=9.95 a,$ where $a$ is the area of the room in square yards.
a. Find $(C \circ a)(x)$ and interpret its meaning in the context of this problem.
b. Find the cost to carpet a square room if its floor dimensions are 15 yd by 15 yd.