If a+b+c=12,a+b=4,and a+c=7 ,what is the value of a?

A 1

B -1

C 3/23

D 2

Correct Answer: Option B

a+b+c=12........(i)
a+b=4.......(ii)
a+c=7...(iii)
(ii)+(iii) 2a+b+11..(iv)
(iv)-(i) a=11-12
অতএব ,a=-1