13. Calculate the product of the polynomial expression

Multiply $31x^2-65y^2$ by $18x^2+42y^2$.

 

 

The resultant product is $i{i}^i+i{i}^i{i}^i-i{i}^i$.

 

[Note: Insert the answer based on terms and its sign and enter coefficient followed by variable and its power. Also, it should satisfy the answer box requirement in alphabetical order.]