Answer:
90
Solution:
Find the difference first
[tex]a_n = a_1 + (n-1)d[/tex]
[tex]54 = 6 + (5-1)d[/tex]
[tex]54 = 6 + 4d[/tex]
Subtract 6 to both sides
[tex]48 = 4d[/tex]
Divide 4 to both sides
[tex]12 = d[/tex]
Since we already found the difference, we can now find the three missing term
[tex]a_2 = a_1 + d[/tex]
[tex]a_2 = 6 + 12 = 18[/tex]
[tex]a_3 = a_2+d[/tex]
[tex]a_3 = 18 + 12 = 30[/tex]
[tex]a_4 = a_3 + d[/tex]
[tex]a_4 = 30 + 12 = 42[/tex]
To get the some (sum), just add the terms.
18 + 30 + 42 = 90
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