Answer
$(0.2x+0.3)^2$
Work Step by Step
The formula for factoring the difference of two cubes is: $A^3-B^3=(A-B)(A^2+AB+B^2)$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $0.04x^2+0.12x+0.09=(0.2x)^2+2\cdot0.2y\cdot0.3+(0.3)^2=(0.2x+0.3)^2$