Not sure if I just don't understand the question, because I find more than one answer possible.

The question is:

Find the nth term of the arithmetic sequence: 7, 12, 17, 22,...

Possible solutions:

a) 5n+2

b) 5n+7

c) 10n+2

d) 10n+7

With (a), I get n=1, 2, 3, 4 which seems to work.

With (b), I get n=0, 1, 2, 3 which also seems to work.

With (c), I get n=.5, 1, 1.5, 2.

With (d), I get n=0, .5, 1, 1.5.