Question 800100
Tn = a+(n-1)d

6=a+(2-1)d
6=a+d
54=a+(4-1)d
54=a+3d

a+d=6
a+3d=54

subtract 
-2d=-48

d=24

if d=24
a=-18


Tn=a+(n-1)d

Tn = -18+(n-1)24

=-18+24n-24

=24n-42