x+4y=-1
3x+y=8

Please see the link posted below.

https://www.askmehelpdesk.com/reading-writing/announcement-font-color-ff0000-u-b-read-first-expectations-homework-help-board-b-u-font.html

Either you change the first equation to:

x= -1 - 4y

Or you change the second equation to:

y= 8 - 3x

The substitute this into the other equation and solve for the last variable.