Answer :

apologiabiology
sum of aritmetic sqeuqnece is
(n/2)(a1+an)
a1=first term
an=nth term
n=how many terms

so we gots
a1=3(1)-4=-1
a18=50
n=18
(18/2)(-1+50)
(9)(49)
441


other one
a1(1-r^(n+1))/(1-r)

2(1-2^(15+1))/(1-(1/4))
 about 2 and 2/3, so closer to 3

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