Binomials coefficients question (1 Viewer)

[Verify]

Not sure how to do this question:
The coefficients of x^4 and x^5 in the expansion (3-x)^n are equal in magnitude but opposite in sign. Find the value of n. I understand what it's asking for but I don't know how to approach it. Thanks.

 

[Carrotsticks]

Find the coefficient of x^4 as you would, using the general term, likewise for x^5.

Equate the coefficients (but chuck a minus sign in front of one of them since we are given that they are negatives of each othr) and you should have an equation that you can solve for n.