A Mixture of Salt and Ice Is Used to Chill

A mixture of salt and ice is used to chill the contents of old-fashioned, hand-operated ice cream makers. What is the melting point of a mixture of 1.00 lb of sodium chloride and 16.00 lb of ice if exactly half the ice melts? Assume ideal behavior and that all the sodium chloride dissolves in the melted ice water. K_f(water) = 1.86°C/m

A) -8°C
B) -11°C
C) -12°C
D) -21°C
E) -15°C