an is the nth term
an-1 is the term before that
we see that
the nth term is obtained by adding 7 to the term before
basically add 7 to each term
an=a1+d(n-1)
d=common difference
a1=first term
given that we add 7 to each term
first term is a1 or -3
an=-3+7(n-1)
an=-3+7n-7
an=-10+7n
an=7n-10
