a2+a9=31
a5-3d+a5+4d=31
2a5+d=31
2*14+d=31
28+d=31
d=3
a5=a1+4d
14=a1+3*4
14=a1+12
a1=2
s12=(a1+a12)*12/2
=(a1+a1+11d)*6
=6(2a1+11d)
=6*(2*2+11*3)
=6*(4+33)
=6*37
=222
a2+a9=31
a5-3d+a5+4d=31
2a5+d=31
2*14+d=31
28+d=31
d=3
a5=a1+4d
14=a1+3*4
14=a1+12
a1=2
s12=(a1+a12)*12/2
=(a1+a1+11d)*6
=6(2a1+11d)
=6*(2*2+11*3)
=6*(4+33)
=6*37
=222