Answer:
71
Explanation:
I am only able to really help with the first part of this question. I am very sorry about that!
Lets take a look at the sequence!
It starts with 3 and then goes to 7. Which means it is adding 4 each time it continues. To confirm this, lets look at 11. 7 goes to 11, which again means it is adding 4! So we understand and now the pattern!
Rather than doing a buttload of work, lets do it an easier way. Lets plug 18 into a calculator!
If you have one, all you need to do is add 3 plus 4. Then plus for again. That should start a ripple effect if you press enter. On the 18 term it would be 71!
Hope that helped.