As per the problem
A first number plus twice the second number is 7
Twice the first number plus the second totals 20
Let the first number is x and second number is y then we can write
[tex] x+2y=7.........(i)\\
\\
2x+y=20........(ii)\\
\\
\text{Now solve these two equations together , multiply equation 1 by 2 }\\
\text{and subtract from equation 2}\\
\\
\ \ 2x+y=20\\
-(2x+4y=14)\\
------\\
-3y=6\\
-----\\
y=-2\\
\text{Substitute this value in equation one we get}\\
\\
x-4=7\\
\\
x=11\\
\\
\text{Hence the two numbers are }\\
x=11, y=-2\\
[/tex]
