+c+1/2a=13 (1)
b+2c+2a=29 (2)
b+3c+9/2a=49(3)
(2)-(1)c+3/2a=16(4)
(3)-(2)c+2.5a=20(5)
(5)-(4)
a=4
带入(4)
c=10
带入(1)
b=1
望采纳