If the 6th term is 22 and the common difference is six, what would your 15th term be?

The 6th term is 22.
The common difference is 6.
Thus the 7th term is 22 + 6.
The 7th term is 28.
The 8th term is 34.
The 9th term is 40.
The 10th term is 46.
The 11th term is 52.
The 12th term is 58.
The 13th term is 64.
The 14th term is 70.
The 15th term is 76.

Here's how you can solve this algebraically if you want to know.
An arithmetic function can be written as 
nth term = common difference × n + starting number

We know that the 6th term is 22, so let's find the starting number.
22 = 6 × 6 + starting number
22 = 36 + starting number
-14 = starting number

Now that we know the starting number, let's find the 15th term.
15th term = 6 × 15 - 14
15th term = 90 - 14
15th term = 76

127 millimeters is the answer