Split the summation to make the starting value of equal to .

Factor out of the summation.

The formula for the summation of a polynomial with degree is:

Substitute the values into the formula and make sure to multiply by the front term.

Simplify.

Add and .

Multiply by .

Divide by .

Multiply by .

Expand the series for each value of .

Simplify.

Simplify each term.

Multiply by .

Multiply by .

Add and .

Replace the summations with the values found.

Subtract from .

Evaluate sum from n=3 to 8 of 5n