Me not shuer weer yu put the blanks, but it look like:
line 1: 2a+5b+c=1
line 2: a+c=2
line 3: b-3c=-3
from line2, c=2-a
put this in line 1...2a+5b+2-a=1 or a+5b=-1
from line 3, b=3c-3=3*(2-a)-3=-3a+6-3=-3a+3
5b=-15a+15
put this intu line1 [a+5b=-1]...a-15a+15=-1
-14a=-16
a=16/14