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Answer 1 · 2017-05-26T23:51:33

#a = 23/2#

#d = -11/4#

We have #a_n = a, (a+d), (a+2d), ... (a+(n-1)d)#

#a_3 = a+2d = 6#

#a_7 = a+6d=-5#

#a=6-2d#

#6-2d+6d=-5#

#4d=-11#

#d=-11/4#

#a+2(-11/4)=6#

#a=23/2#

From here, finding the required terms is elementary.