Question 1084676
an=a1+(n-1)d
d=3, between 7th and 8th term
a7=a1+(n-1)d
a7=a1+6*3=a1+18
19=a1+18
a1=1
a40=1+(39)*3=118
sum=(40/2)(a1+a40)=20+(1+118)=119*20=2380