A is 2 yr younger than B and B is 3 yr younger than C. What is the age of A, B, C? 2. If the total age of A, B, C is 72 yr, what is the age of each. For the given question 1, answer the question 2.

Initial number of people ($P_1$) = 18
Initial duration of food ($D_1$) = 10 days
Days passed ($D_p$) = 2 days
Number of people who left ($P_L$) = 6

This directly answers part (a).
The decrease in the number of people is the number of people who left.

a) The decrease in the number of people is $\boxed{\text{6 people}}$.

After 6 people left, the number of remaining people ($P_2$) is:

Part (b) asks for the total food for the remaining 7 days. This refers to the amount of food (in person-days) that the remaining 12 people would consume over a period of 7 days.

b) The total food for the remaining 7 days is $\boxed{\text{84 person-days}}$.