We can rewrite this expression as:
(0.1x + 0.4y)(0.1x + 0.4y)(0.1x+0.4y)(0.1x+0.4y)
To multiply these two terms you multiply each individual term in the left parenthesis by each individual term in the right parenthesis.
(color(red)(0.1x) + color(red)(0.4y))(color(blue)(0.1x) + color(blue)(0.4y))(0.1x+0.4y)(0.1x+0.4y) becomes:
(color(red)(0.1x) xx color(blue)(0.1x)) + (color(red)(0.1x) xx color(blue)(0.4y)) + (color(red)(0.4y) xx color(blue)(0.1x)) + (color(red)(0.4y) xx color(blue)(0.4y))(0.1x×0.1x)+(0.1x×0.4y)+(0.4y×0.1x)+(0.4y×0.4y)
0.01x^2 + 0.04xy + 0.04xy + 0.16y^20.01x2+0.04xy+0.04xy+0.16y2
We can now combine like terms:
0.01x^2 + (0.04 + 0.04)xy + 0.16y^20.01x2+(0.04+0.04)xy+0.16y2
0.01x^2 + 0.08xy + 0.16y^20.01x2+0.08xy+0.16y2