What is the summation notation of quantity of 3a plus 4a plus 5a plus 6a to the third power?

Answer 1

It is not clear whether the question is

3a + 4a + 5a + 6a^3 which would be 12a + 6a^3

or 3a + 4a + 5a + (6a)^3 = 12a + 216a^3

or (3a + 4a + 5a + 6a)^3 = 5832*a^3

But none of these really require summation notation!

Answer 2

Replace the number with "n"; so the term to be summed (to the right of the summation sign) would be "na to the third power", to the third power. Below the summation sign you write the variable and the lower limit, n=3. Above the summation sign you write the upper limit, 6.