Answer
$x^4+12x^3y+54x^2y^2+108xy^3+y^4$
Work Step by Step
$(x+3y)^4$
$x^4+4x^3(3y)+6x^2(3y)^2+4x(3y)^3+y^4$
$x^4+12x^3y+6x^2(9y^2)+4x(27y^3)+y^4$
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