We have the following expressions:
[tex]\begin{gathered} A=7x^3+3x^6-3 \\ B=7x^6-3-7x^3 \end{gathered}[/tex]We have to calculate:
B+A
Replace the values:
[tex]B+A=(7x^6-3-7x^3)+(7x^3+3x^6-3)[/tex][tex]7x^6-3-7x^3+7x^3+3x^6-3[/tex]Add and subtract the alike terms ( the ones with the same variable and exponent, for example, 7x6 and 3x6)
You can order the terms from highest exponent to lowest,
[tex]7x^6+3x^6-7x^3+7x^6-3-3[/tex]Then add and subtract
[tex](7x^6+3x^6)+(-7x^3+7x^3)+(-3-3)[/tex][tex](10x^6)+(-6)[/tex][tex]10x^6-6[/tex]