Explanation:
we see the common difference is
a2-a1 = 11x + 9 - 4x - 5 = 7x + 4
an = an-1 + (7x+4) = a1 + (n-1)×(7x+4)
for a7 we have then
a7 = 4x + 5 + 6×(7x +4) = 4x + 5 + 42x + 24 = 46x + 29
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