Answer
$25y^2-4x^2-12x-9$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
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: $[5y+(2x+3)][5y-(2x+3)]=(5y)^2-(2x+3)^2=25y^2-(2x)^2-2\cdot2x \cdot3-3^2=25y^2-4x^2-12x-9$