Question 912112
We don't know the total invested.
We know the difference in the two accounts.
We know that the interest for the two accounts is $670
0.05*x+0.04*y=670
We know that the account at 5% has $800 more.
x=800+y
We substitute for x
0.05*(800+y)+0.04*y=670
We multiply out
40+0.05y+0.04*y=670
We combine like terms.
0.09*y=630
Isolate y
y=$7000 at 4%
x=800+y
Calculate x
x=$7800 at 5%
Now,we know the total invested is: 14800
Total invested $7800+$7000=$14800
We check
0.05*7800+0.04*7000=670
390+280=670
670=670
Since this statement is TRUE and neither x nor y is negative all is well.
codeintmt


But you want it solved using elimination or addition

0.05*x+0.04*y=670
x=800+y
x-y=800
0.05*x+0.04*y=670
multiply by 100 
5*x+4*y=67000
x-y=800
multiply by 6
4x-4y=3200
5*x+4*y=67000
add
9x=70200
x=7800 at 5%
y=7000 at 4%