$(\color{red}{4x}+\color{green}{y})^2
\,$ $=\,(\color{red}{4x})^2 \,+ 2\times\color{red}{4x}\times\color{green}{y} \,+ \color{green}{y}^2$ $= $ ?
$-16\,x^2\, +8\,x\,y\,+ \,y^2$ $16x\, +8\,x\,y\,+ \,y^2$ $4\,x^2\, +8\,x\,y\,+ \,y^2$ $16\,x^2\, +8\,x\,y\,+ \,y^2$