<PRE><B>Question 843458</B>
Hey!

T4= a+3d =7  ----- (1)
T9= a+8d =17 ----- (2)

(2)-(1)
Therefore 5d = 10
d=2 


a+ 6= 7
Therefore a = 1

T15= a+14d
T15 = 1 + 14(2) = 29

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