There is no problem on here
The answer is z=2m+3 so the first one is right
Ok so what you will do is 3-18 then you will add 1 and make is to 400X1
3,857:
1. 3 is located in the thousands place
2. Since 8 is bigger than 3, it's telling it to go up a number (turning 3 into a 4)
Stays the Same: 1,2,3,4
Goes Up: 5,6,7,8, etc.
So 3,857 is now rounded into 4,000