Afirst number plus twice a second number is 5.twice the first number plus the second totals 31.find

So if I understand this correctly, this would look something like this:

A first number

let's call it x

 plus twice a second number

let's call the second number y:

x+2y=5

 is 5.

this means that x=5-2y!

twice the first number plus the second totals 31.

2x+y=31

from the last one, i know that y=31-2x

and i can insert it into the first equation:

So i know that x=5-2y

and that

2x+y=31
i will substitute x here

2(5-2y)+y=31

remove the bracket

10-4y+y=31

10-3y=31

remove 10 from both sides

-3y=21

then

y=-7

and
x=5-2(-7)=5+14=19