Formula use: \left(a+b\right)^3=a^3+3.a^2.b+3.a.b^2+b^3
Explanation
Here, given expression is : 5x+3y
Now, we find the cubes with the help of formula :
\left(5x+3y\right)^3
\rightarrow\left(5x\right)^3+3.\left(5x\right)^2.3y+3.5x.\left(3y\right)^2+\left(3y\right)^3 [use formula]
\rightarrow 125x^3+225x^2y+135xy^2+27y^3
Ans: 125x^3+225x^2y+135xy^2+27y^3\ .