A 20 Cm Diameter Balloon at 1atm and 21 ^$\circ$ C Is Cooled Until Its Diameter Shrinks to 18 Cm

A 20 cm diameter balloon at 1atm and 21 ^$\circ$ C is cooled until its diameter shrinks to 18 cm.What is the final temperature of the gas in the balloon?

A) 19 ^$\circ$ C
B) 0 ^$\circ$ C
C) 21 ^$\circ$ C
D) -21 ^$\circ$ C
E) -59 ^$\circ$ C