Status: Waiting for your answers. Problem:Find the sum of the first 135 multiples of 5. Plan:Find the first three terms and last term of the series.Use the sum formula to calculate the sum of the series, S_{135}. Step 1: a_{1} + a_{2} + a_{3} + ··· + a_{n} + + + ··· + Step 2:S_{135} =