By the distributive property:
#color(white)("XXX")color(blue)a(color(green)b+color(orange)c+color(magenta)d) = color(blue)acolor(green)b+color(blue)acolor(orange)c+color(blue)acolor(magenta)d#
So
#color(white)("XXX")color(red)(5x^2)(color(blue)(5x^2)+color(orange)(7x)+color(magenta)3) =color(blue)(5x^2) * color(green)(5x^2)+color(blue)(5x^2) * color(orange)(7x)+color(blue)(5x^2) * color(magenta)3#
#color(white)("XXXXXXXXXXXXXX")=25x^2 color(white)("xxx")+35x^3color(white)("xxx")+15x^2#