Formula use: \left(a+b\right)^3=a^3+3.a^2.b+3.a.b^2+b^3

Explanation

Here, given equation is :
\left(3x+5y\right)^3+3\left(3x+5y\right)^2\left(2x-5y\right)+3\left(3x+5y\right)\left(2x-5y\right)^2+\left(2x-5y\right)^3
Let,
\left(3x+5y\right)=a
\left(2x-5y\right)=b
So that, we get :
a^3+3{.a}^2.b+3.a.b^2+b^3
\rightarrow\left(a+b\right)^3
Now putting the value :
\{\left(3x+5y\right)+\left(2x-5y\right)\}^3
\rightarrow\left(3x+5y+2x-5y\right)^3
\rightarrow\left(5x\right)^3
\rightarrow125x^3
Ans: 125x^3\ .