The answer would be 8000.
The formula of an arithmetic sequence is the following :

A geometric sequence is in the form:
You have to plug in the numbers.
So first let's plug in 13. 7*13+8=99
Now 15. 7*15+8=113
Now 18. 7*18+8=134
Lastly 20. 7*20+8=148
The answer is 13.
A kg is 1000 grams, so you would 1000*4.