a5=a1+4d
a9=a1+8d
3=a1+4d
15=a1+8d
3-4d=15-8d
-4d+8d=15-3
4d=12
d=3
a1=3-4*3= 3-12= -9
S30= (2a1+29d)/2*30= 15*(-18+87)= 15*69=1035
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a5=a1+4d
a9=a1+8d
3=a1+4d
15=a1+8d
3-4d=15-8d
-4d+8d=15-3
4d=12
d=3
a1=3-4*3= 3-12= -9
S30= (2a1+29d)/2*30= 15*(-18+87)= 15*69=1035