To start off with y being positive we have to leave it on the left of = and move everything else.
Add color(blue)(4x)to both sides. This turns the -4x on the left into 0 and you end up with it on the right of = but being positive.
color(brown)(-4xcolor(blue)(+4x)+5y+16= 0 color(blue)(+4x))
0+5y+16=4x
Subtract color(blue)(16) from both sides
color(brown)(5y+16color(blue)(-16)=4xcolor(blue)(-16))
5y+0=4x-16
Divide both sides by color(blue)(5). This turns the 5 from 5y into 1 as 5/5=1" and " 1xxy=y
color(brown)(5/(color(blue)(5))xxy=4/(color(blue)(5))x-16/(color(blue)(5))
y= 4/5x-16/5