Q: 117 (CAPF/2014)

In a family, the age of father, mother, son and grandson are A, B, C and D respectively. Given that A - B = 3, B + C = 78, C + D = 33 and the average age of the family is 34 years, then B - C is :
question_subject: 
Maths
question_year: 
2014
question_exam: 
CAPF
stats: 
0,88,112,48,40,24,88