i am trying to add 8.5 over and over again so in essence 8.5 x2 then 8.5 x 3 8.5x4 what is the fastest way to do this.

$$\sum_{n=0}^{\infty} 8.5n=\infty$$

However 

8.5+2*8.5+3*8.5.......n*8.5

is the sum of a geometric series

a=8.5

r=8.5

$$\\s_n=\frac{a(r^n-1)}{r-1}\\\\
s_n=\frac{8.5(8.5^n-1)}{8.5-1}\\\\
s_n=\frac{8.5(8.5^n-1)}{7.5}\\\\$$

I think I got the formula right. 

If you need sum of it use gauss theorem 8,5(1+2...x)=8,5(x.x+1/2)