A Bio hardy weinberg question, asking about the frequency of a certain allele.

A moth has three alleles at a locus that controls antenna color: X1, X2 and X3. X1 is dominant to X2 and X3;
X1 produces red antennae. X2 is co-dominant to X3; X2X2 produces yellow antennae, X3X3 produces white
antennae, and X2X3 produces light yellow antennae. The phenotypic frequencies in a population are as follows:
0.04 WHITE 0.16 LIGHT YELLOW 0.16 YELLOW 0.64 RED
⇒ Assuming that this population is in Hardy-Weinberg equilibrium, what is the frequency of the X3
allele in this population?
a) 0.04
b) 0.20
c) 0.16
d) 0.32
e) 0.64

B

Well i just typed out a whole bunch of work and systems of equations, but I'm dumb. Really, you can just show:

(X3)^2=0.04
X3=0.2

and get the answer