Question 183584
c=b+4
b=3(a+1)
c=2a+7 replace c with (b+4)
(b+4)=2a+7
b=2a+7-4
b=2a+3 
now replace b in this equation with 3(a+1)
3(a+1)=2a+3
3a+3=2a+3
3a-2a=3-3
a=0 ans.
b=3(0+1)
b=0+3
b=3 ans.
c=2*0+7
c=7 ans.