Phương trình vi phân : y''-4y'=e^3x

Need on this one asap im almost done with this subject

Write the equation for the parabola that has x− intercepts (−2,0) and (4,0) and y− intercept (0,4).

Write a polynomial function f of least degree that has rational coefficients, a leading coefficient of 1, and the given zeros. 3, 4+2i, 1+(sqrt)7 the answer is supposed to be: f(x)=x(^5)-13x(^4)+60x(^3)-82x(^2)-144x+360 what am i doing wrong?