Help with reworking an equation

The equation was x+y= 600
5x+10y= 4750
And I was told to find the solution
Now I have to rework the system where instead of 600 its 800
And I don't know how to
Please help
Please and thank you
L0V£

so this is
x+y= 800
5x+10y= 4750
??

multiply first by –5 and add
–5x–5y = –4000
5x+10y= 4750
5y = 750
y = 150

x = 800–y = 800–150 = 650

check
5x+10y= 4750
5•650 + 10•150 = 4750
3250 + 1500 = 4750 ok

x+y= 600 eqn 1 ----> y = 600 - x
5x+10y= 4750 eqn 2
Substitute eqn 1 into eqn2 and solve