X+y = 4, therefore y = 4-x when you rearrange the equation.
You can subsitute this in: x-(4-x) = 6
-4+x = 6-x
x=10-x
2x = 10
x = 5
Substitute x into the previous equation:
5+y = 4
y = 4-5
y = -1
This is simple division to do this you must know you multiplication. However the answer is 28 ;)
Alright.
So, we have 2185 student in Rose.
Lily School has 307 more students than Rose, so Lily has,
2185 + 307 = 2492 Students in Lily School.
Since question a. is asking you to round off to the nearest ten, your answer to part a is 2490.
For part b. add 2185 and 2490.
2185 + 2490 = 4675 students.
The questions want you to round to the nearest hundredth, so,
4700 is the answer to part b.