So based on place values, the One's place is occupied by 4. To round to this digit, you go one number to the right. If that number is 5 or higher, you add one to 4. If it is less than 5, you don't add any to 4. Since 7 is greater than 5, you add 1 to 4, giving you 5, since you can now remove all the other numbers to the right.
5.
Answer: 19 booooooooooiii
From the second:
2x-y=4
x=(4+y)/2 and applying this to first:
4+y+3y=12
4y+4=12
4y=8
y=2 and since x=(4+y)/2, x=3 so
x+y=2+3=5
