(a+109)*30=6510
30a + 3270 = 6510
30a = 6510 - 3270
30a = 3240
a = 3240/30
a = 108
d-(240*13)=1260
d - 3120 = 1260
d=3120+1260
d=4380
n+1240=1060*20
n+1240=21200
n=21200-1240
n=19960
(a+109)*30=6510
30a + 3270 = 6510
30a = 6510 - 3270
30a = 3240
a = 3240/30
a = 108
d-(240*13)=1260
d - 3120 = 1260
d=3120+1260
d=4380
n+1240=1060*20
n+1240=21200
n=21200-1240
n=19960