#1. Just plug in the vales for n: 1,2,3,4,5 ...
a_1 = 6*1 + 1 = 7
and so on
shucks -- I guess that narrows down the choices, yeah?
#2. Just keep subtracting 2
a_1 = 8
a_(n+1) = a_n - 2
#3. clearly there is a common difference of 7
so a_n = a + (n-1)d = -13 + 7(n-1)
better review your AP section.